I think I've got quite a good long term fix for the vault space issue. Most people just want more squares; but that won't work in 5 years time. This idea will:
Completely scrap the current vault model and replace it with a multi-page list of weapons/ armor/ misc. Each "tab" will contain maybe 5-10 pages for each category (weapons, armor, misc), with enough space for probably 50+ "items" of that category per page. Difference is, there will be no pictures of each item listed; only the name of each item. Moving your cursor over a certain item name will expand the details of said item. The picture of the selected item could be shown, description, statistics, perk details. Hell, everything could be shown because you're only viewing [b]one[/b] item.
This would eliminate the issue of too many weapons being shown on screen at once because at any given time you could only be viewing one picture of an item alongside a crap ton of text (which shouldn't be too hard on the console: even last gen). This would also be an excellent long term fix, having addressed the "too many pictures on screen at once" issue. The only issue now would be how many items they could store per player on their databases. Which you'd think would be fairly large considering this game is just planning to get bigger and bigger.
Hopefully something along these lines (or at least the multi-page vault) will be made in the future. Something large that will endure the years of us playing this game to come. I don't know about you, but I'd like to still have at least a few of my vanilla Destiny weapons in a few years time (assuming they're just adding giant expansions and not entirely new games).
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Possibly impossible. As stated before xb360 and PS3 are holding next gen back. Their new vault system consists of vendors 'holding onto' weapons you unlocked so you can pick them up any time.