Was looking through the Inventory API used for chests and comparing it to CC:T's it seems very out of date. At present if I were to, say, make a peripheral that provides the inventory/ender chest of a player I really couldn't easily do that.

Furthermore, we have mods like Industrial Revolution, Tech Reborn, and Applied Energistics that provide different APIs that should be hooked into for the energy category of generic peripherals.

References:
CC:R InventoryMethods
CC:R InventoryUtil
CC:T Inventory Methods
CC:T InventoryUtil

if I were to, say, make a peripheral that provides the inventory/ender chest of a player I really couldn't easily do that.

I think hugeblank/cc-tweaked-fabric@b6589b3 fixes this. It's just a 3 line fix that adds inventories into consideration when evaluating things that can be wrapped with the ItemStorage wrapper.