I was just thinking about Ghost Rider, and was thinking how could it would be (at least for me) if Blackheart returned.
Also, on the whole Infinity Gems/Stones talk:
Power: Damage Increase
Space: Super Armor
Soul: Life Recovery
Time: Speed Increase
Mind: Meter Regeneration
Reality: ?
From MHS.
Different characters got specific boosts depending on the gem as well.
Wolverine: Power Gem basically gives him Berserker Charge
Juggernaut: Space Gem gave him true Super Armor
Magneto: Space Gem gives him his forcefield
Spider-Man: Power Gem gives him a clone of himself that mirrors his movements, and ups his damage
Blackheart: Reality Gem turns him invisible for a few seconds
Hulk: Time Gem gave him the ability to throw extra fast Heavy attacks
Psylocke: Power Gem gave her clones
Shuma-Gorath: Time Gem lets his attacks turn you to stone
Captain America: Power Gem gives him multi hit Shield Slash, Stars & Stripes, and Charging Star
Iron Man: Soul Gem gave his attacks electricity which drained your meter and refilled his life faster
So maybe Gems in MVCI will grant specific bonuses to certain characters.