Currently, Bukkit.createInventory(...) returns a CraftInventoryCustom. I think it would be better for it to return a class matching chosen InventoryType, Just like world.spawnEntity does.
For example:
ANVIL=> AnvilInventory
CRAFTING => CraftingInventory
ENCHANTING => EnchantingInventory

This would give us access to more fuctions, like getRenameText in AnvilInventory, which we can only get by using CraftAnvilInventory.