So I have a proposition for a possible resolution to the ever present vault space issue. Hear me out what if we don't have a vault? But the collections become our vault. Oh but what about my 7 plus rolls of chroma rush or my ten different chest pieces with different stats for different builds? Well currently in collections no random rolls can be obtained which is fine but what if we can still re obtain the rolls you've gotten? Ahhh see where I'm going? You can remove vault entirely and in collections you can re obtain any gear but only rolls you've had already there's only so many combos of each piece of gear.
TLDR; Ditch vault re obtain any previous item rolls in collections issue resolved. Let's make it work.