While I think there will still be a limit to the Vault, my personal hope is that Destiny 2 introduces a revamped kiosk system.
Instead of multiple kiosks for different things (exotics weapons, exotic armor, holiday loot, emblems, ships, etc.), they will have a single kiosk (placed in multiple areas) that tracks all of that.
And not just all of what there were already kiosks for in Destiny 1 but it would track literally every piece of loot in the game, from the obvious exotic loot all the way down to green and grey common and uncommon loot.
It would let you grab something you previously had to delete whenever you want while also simultaneously acting as a catalog/checklist for completionists like myself.