I think Item Burden should return, but not in the way it was in Demon's Souls:
First, the bottomless box should stay so you don't have to depend on an NPC and then enter "hardcore" mode because you accidentally provoked him in the beginning of the game.
It's simple, you have a fixed limited inventory space. This is not based on weight, but rather actual space. You can only carry 4 weapons, 10 pieces of armor, 4 rings, 999 arrows, 20 items (not including souls) and 99999 pieces of ore. (Unlimited really). Not to be taken as values I want, but rather I suggest as an example. If you pick up an item that would exceed this limit, you can decide to either:
1) Send it to the Bottomless Box
2) Send an item you currently have to the Bottomless box
Just my take on Item Burden returning. Cause right now, we are a breathing armory. We don't need to think much ahead because we have everything at our disposal all the time with the exception of magic.