When combined with @Optional this should address all issues of soft dependancy on mods/apis.
This also addresses the issue of dynamic functionality in TileEntities/Entities.
Current capability providers: TileEntity, Entity, ItemStack
Also added INBTSerializeable, a generic interface for game objects that can be written to/from NBT tags.
Vanilla capabilities will be coming soon, mostly on request and review.
So start requesting capabiliteis on vanilla/Forge features.