I like the idea, I just see it hard to execute in Destiny mostly because of PvP. One of their big hurdles is keeping weapons tuned for both PvP and PvE. I think whichever class you give Hand Cannon buffs becomes the only class people use in PvP. I could be wrong, it could be done well if tuned well. It's definitely an interesting idea though since each character will soon have three classes. You'd get coverage of 9 weapon types (AR, HC, Pulse, Scout, Fusion, Shotty, Sniper, Machine, Rocket).
This is turning into dreamland but they could be tied to existing perks. For instance when you hit someone or something with a throwing knife if you have a fusion rifle equipped it automatically charges your weapon for instant firing. It's not this long lasting perk that is ever present, something that requires skill to trigger, and is only temporary. A more subtle implementation of this across the board.