I think many of us are collectors, and I think I have a pretty good idea on how to give us more vault space, without actually increasing vault space. Give us each our own personal space in the tower/reef/Felwinter's Peak, where we keep the endgame items we've gotten only from raids/POE/IB/ToO. As we get them, each one fills up a designated spot in our personal space. Sort of like a trophy room. This way we can keep full sets these weapons/armor without having to worry about vault space. So you could have the entire VoG and Crota's End sets, without taking up 18 weapon slots and 8 armor slots in the vault. But here's the catch - you can only keep one of each, per character. Any addition items (such as a second helmet with different perks) is now held in the vault. These items are a sign of our accomplishments from the first 2 years of Destiny - we shouldn't have to consider trashing them because there are more powerful weapons that we need to make room for in the vault.