To be honest I think that Xur (even though has hasn't sold every item) is already a decent balance to RNG. It might be nice to incorporate some sort of a token system for raid only gear as even with the 'smart loot' in TDB there are still many people who are chasing that last piece (or pieces) of loot that elude them. For example: I've gotten about 15 Hunger of Crota's but not one Black Hammer. I think it would be cool to have open world mini-bosses that have set loot tables that include legendary gear much like in the E3 2013 vidoc but it would be more of a flavor aspect than an actual loot balancing thing.