Ouch. I refused to part with my Shadow Price and TDYK for this very reason. Hey, maybe Bungie will put them back up for sale once they become upgradeable. As for Vault limitations, I couldn't say for sure without seeing the code, but I suspect it's mostly due to having the Tower loaded in the background taking up RAM. I only played around with Skyrim's mod tools a bit, but basically it loaded the world in small instances and chunks and just showed static images of everything else (so that mountain range up ahead is really just a picture of it until you get close enough for the real thing to load) and most player storage was inside, which means in a much smaller instance. It also froze everything else while you were in storage (a luxury online games don't have). In contrast, Destiny has the whole tower loaded up in RAM at once. The system has to keep track of 16 players, their movements, their equipped gear, your inventory, your items' stats, your vault, all the NPCs, and everything else going on in the tower. Normally, this wouldn't be an issue except that Destiny is already strenuous on older systems for whatever reason (as evidenced by the menu load times). The older systems just don't have the RAM to spare for more vault stuff being displayed.