perhaps you can make it to where packs are not insert-able into other packs. But to alleviate the loss of what is infinite capacity perhaps add hand carts(and/or horse carts if mounts are added) that have say 6 slots for non stack-able packs. and then maybe add other carts say one with a cage on it?anyways, that's just an idea.
P.s. I am rather new so i apologize if someone else has brought this up.