All rarities/ways to obtain/etc are fully up to Brass if any of these ideas are decent enough.
Rune of Variance
This Rune will allow you to re-roll both the stats and a suffix' stats (if applicable) on the gun of your choice. E.G: Stats will change their variables depending on what the Tier allows, and Suffix' will get a different chance/duration/damage/etc. This could be bad or good!
Rune of Reincarnation
This Rune will reset your level to 1, letting you gain EXP to get more Gift Packages. If you reset above level 50, you get a permanent "Perk" that causes the Gift Packages you open to count as +5 levels over what you currently are. (E.G the level 5 package will count as a level 10). Getting to level 60 before resetting, no matter which "Reset" it is, would make the bonus +10. Getting to level 70 would make it +15.
Rune of Refreshing
This Rune will cause your Event Cool-downs to immediately reset, thus allowing you to play them again. This could either affect one Event if there are multiple and they don't share the cool-downs, or just a specific one.
Rune of Fashion (New idea from Kili, thanks!)
This Rune would give you a random 3x3 panel similar to the Gift Package, but inside of it would be 9 of -ANY- cosmetic ever released. Obviously, rarer ones would show up much less often. You get to pick -1- cosmetic from these 9. You can NOT get Exotic accessories from this! (Good thinking, Dread.)
Rune of Progression
This Rune will cause you to gain some %, or when at low levels possibly even a level, in an Enchancable weapon of your choice. This effect will be immediate and unusable if the Weapon is currently maxed-out. (I feel its unfair for a handful of players to have maxed-out weapons when they leveled up quite literally a hundred times faster, this could give a little boost to the more unlucky players?)
Rune of Disappointment (Small Credits to Kuro!)
When used, the next Gift Package to be empty will re-roll itself to give you another chance!
Rune of Transmogrification
This Rune, after being used, will turn a weapons crate into another Crate of any type. (I figured if these Runes weren't super common, then it'd be kinda neat.)
Rune of Empowerment
After being used, EXP gains AND EXP losses are increased by +100% for four hours. This could possibly count for leveling up weapons, too?
Rune of Tricksters
After being used, for every round that you don't get a drop, you get an increasing chance to get a drop. It will eventually hit 100%.
Rune of Wealth
For a set amount of rounds, your minimum drops is raised slightly higher. (Expect to not be able to drop commons, and instead they'd be uncommons?)
Rune of Wonders
For X rounds after using this Rune, there is an increased chance of all mini-games to happen.
Rune of Artifacts
This Rune would be quite a bit more unique than most. For some time after use, For every "Standard" round that your team wins (6+ people on minimum), you'll gain a "charge". You can expend the charges to act as a random roll. The more charges that you have, the better items that you can get.
Rune of Fragmentation
Upon use, the Rune is consumed and you get to choose up to five items to destroy. These items will be 100% unrecoverable, but you will get a (Very) small amount of Forerunner Fragments. More rare weaponry will, of course, give better returns. Crystals can NOT be used! (Good idea, Leo.)
Rune of Scales
Once used, a Dragon Round will happen the next immediately available round. You have a much higher chance to be the Dragon, but not absolute.
Rune of Subterfuge
When used, the next immediately available round will be a Hunter round. You have a much higher chance to be the one chosen as a Hunter, however, it isn't a guarantee.
Rune(s) of Unlocking
There are four tiers of these runes; and they can replace (3) of the items required to create a Key by themselves. You can get Tier I, II, III and IV, but no higher.
Rune of Ability
A special Rune. When used, it will double the EXP cost required to level up a gun, but will grant (1) bonus MAXIMUM Enhancement to it. This may possibly be done multiple times if it isn't too overpowered, but each time will add even more EXP cost. The first rune is 2x, the second is 5x, the third is 9x, etc, until it would become nearly impossible to level up. (If this doesn't work or just would be overpowered, maybe any gun that is not unique and legendary or below could gain an Enhancement Point with high XP costs, just to -slightly- customize your favorite weapon?)
Rune of Charging
You may use this Rune to charge any crystal with 2-6 full charges. [E.G an empty crystal could become Blaze Crystal(5).]
Rune of Leprechauns
After using this Rune, for every 30 minutes you play in a row you will gain a random coin drop, most likely not breaking several hundred. This Rune will last from (1) hour to (6) hours, which only "Counts down" when you play. Spectator does NOT count.
Rune of Power
When used, for the rest of the map you will be equipped with a random Godlike primary, secondary and melee if applicable. These are drop-able, but otherwise disappear upon re-equipping/etc. (Figured it'd be fun for someone to get to play around with Godlikes that they may never get. Plus, RNG!)
Rune of Marriage
Upon use, Kcat immediately marries you. Only one may drop. I call dibs!
More to come?
Other Rune-Related Ideas
Bag o' Runes
A rare chance to appear in a Forerunner Fragment shop, this bag will contain 2-6 random Runes at a -moderately- high price of Fragments.
Sack o' Runes
A very rare reward from a Gift Package, this contains 1-3 random runes!
Ways to obtain Runes
Just getting Runes as a drop would be boring. There should be a way to drop Fragments to craft Runes of your choice. Fragments will come in a few varieties, and obtainable in different ways. E.G: Fragment 1's would drop from Morgath only, while Fragment 2's could be found in Crates. Fragment 3's would be obtainable from end-round drops, etc.
Rune of Variance
This Rune will allow you to re-roll both the stats and a suffix' stats (if applicable) on the gun of your choice. E.G: Stats will change their variables depending on what the Tier allows, and Suffix' will get a different chance/duration/damage/etc. This could be bad or good!
Rune of Reincarnation
This Rune will reset your level to 1, letting you gain EXP to get more Gift Packages. If you reset above level 50, you get a permanent "Perk" that causes the Gift Packages you open to count as +5 levels over what you currently are. (E.G the level 5 package will count as a level 10). Getting to level 60 before resetting, no matter which "Reset" it is, would make the bonus +10. Getting to level 70 would make it +15.
Rune of Refreshing
This Rune will cause your Event Cool-downs to immediately reset, thus allowing you to play them again. This could either affect one Event if there are multiple and they don't share the cool-downs, or just a specific one.
Rune of Fashion (New idea from Kili, thanks!)
This Rune would give you a random 3x3 panel similar to the Gift Package, but inside of it would be 9 of -ANY- cosmetic ever released. Obviously, rarer ones would show up much less often. You get to pick -1- cosmetic from these 9. You can NOT get Exotic accessories from this! (Good thinking, Dread.)
Rune of Progression
This Rune will cause you to gain some %, or when at low levels possibly even a level, in an Enchancable weapon of your choice. This effect will be immediate and unusable if the Weapon is currently maxed-out. (I feel its unfair for a handful of players to have maxed-out weapons when they leveled up quite literally a hundred times faster, this could give a little boost to the more unlucky players?)
Rune of Disappointment (Small Credits to Kuro!)
When used, the next Gift Package to be empty will re-roll itself to give you another chance!
Rune of Transmogrification
This Rune, after being used, will turn a weapons crate into another Crate of any type. (I figured if these Runes weren't super common, then it'd be kinda neat.)
Rune of Empowerment
After being used, EXP gains AND EXP losses are increased by +100% for four hours. This could possibly count for leveling up weapons, too?
Rune of Tricksters
After being used, for every round that you don't get a drop, you get an increasing chance to get a drop. It will eventually hit 100%.
Rune of Wealth
For a set amount of rounds, your minimum drops is raised slightly higher. (Expect to not be able to drop commons, and instead they'd be uncommons?)
Rune of Wonders
For X rounds after using this Rune, there is an increased chance of all mini-games to happen.
Rune of Artifacts
This Rune would be quite a bit more unique than most. For some time after use, For every "Standard" round that your team wins (6+ people on minimum), you'll gain a "charge". You can expend the charges to act as a random roll. The more charges that you have, the better items that you can get.
Rune of Fragmentation
Upon use, the Rune is consumed and you get to choose up to five items to destroy. These items will be 100% unrecoverable, but you will get a (Very) small amount of Forerunner Fragments. More rare weaponry will, of course, give better returns. Crystals can NOT be used! (Good idea, Leo.)
Rune of Scales
Once used, a Dragon Round will happen the next immediately available round. You have a much higher chance to be the Dragon, but not absolute.
Rune of Subterfuge
When used, the next immediately available round will be a Hunter round. You have a much higher chance to be the one chosen as a Hunter, however, it isn't a guarantee.
Rune(s) of Unlocking
There are four tiers of these runes; and they can replace (3) of the items required to create a Key by themselves. You can get Tier I, II, III and IV, but no higher.
Rune of Ability
A special Rune. When used, it will double the EXP cost required to level up a gun, but will grant (1) bonus MAXIMUM Enhancement to it. This may possibly be done multiple times if it isn't too overpowered, but each time will add even more EXP cost. The first rune is 2x, the second is 5x, the third is 9x, etc, until it would become nearly impossible to level up. (If this doesn't work or just would be overpowered, maybe any gun that is not unique and legendary or below could gain an Enhancement Point with high XP costs, just to -slightly- customize your favorite weapon?)
Rune of Charging
You may use this Rune to charge any crystal with 2-6 full charges. [E.G an empty crystal could become Blaze Crystal(5).]
Rune of Leprechauns
After using this Rune, for every 30 minutes you play in a row you will gain a random coin drop, most likely not breaking several hundred. This Rune will last from (1) hour to (6) hours, which only "Counts down" when you play. Spectator does NOT count.
Rune of Power
When used, for the rest of the map you will be equipped with a random Godlike primary, secondary and melee if applicable. These are drop-able, but otherwise disappear upon re-equipping/etc. (Figured it'd be fun for someone to get to play around with Godlikes that they may never get. Plus, RNG!)
Rune of Marriage
Upon use, Kcat immediately marries you. Only one may drop. I call dibs!
More to come?
Other Rune-Related Ideas
Bag o' Runes
A rare chance to appear in a Forerunner Fragment shop, this bag will contain 2-6 random Runes at a -moderately- high price of Fragments.
Sack o' Runes
A very rare reward from a Gift Package, this contains 1-3 random runes!
Ways to obtain Runes
Just getting Runes as a drop would be boring. There should be a way to drop Fragments to craft Runes of your choice. Fragments will come in a few varieties, and obtainable in different ways. E.G: Fragment 1's would drop from Morgath only, while Fragment 2's could be found in Crates. Fragment 3's would be obtainable from end-round drops, etc.