Also there wouldn't be much more memory limitations. Chances are, they're using an integer to store the max quantity for your vault. An integer is about 4 bytes and can be any number between -2.14 billion to 2.14 billion. No matter that number you pick in between, it's still only 4 bytes. What WOULD make more vault space hard is load times. You'd have to send a request to the server, pack all that data for the gear in your accounts data table, send/receive it and then display it in a proper time span and without breaking the bank on decent servers and a proper bandwidth allowance. That is the reason we don't have more space. Bungie probably doesn't see a reason to update game servers for a 3 year old game that'll be obsolete in 6 months.