Just a question:
Currently the core weight logic is based on Items not ItemStacks. (Refer to ArmorHandler.getArmorWeight.) Is it possible to have this API accept an ItemStack?

Case: I would like to provide a Feathers-plugin for the ArmorUnderwear mod; however, I cannot mixin at this method successfully as the stack has been stripped (and that's where all the goodies regarding armor alterations are kept.) This might require some changes to how feathers info sent from client and everything seems item-id based.

I think this would be nice as well. If the API can read an ItemStack, then it could derive weight for armor from, say, Truly Modular's stuff.