Since you don't get armour from raids (which is generally where a lot of people get exotics from) then I believe xür selling them isn't a huge deal. Armour isn't incredibly special anyway. Xür should just take weaponry off his loot table. I've played about 700 hours now and have exotic weapon besides the gjallarhorn and necro. But I still think it's best he doesn't sell gjallarhorn or anything else to be honest. Relying on rng means that people actually use different weapons. Just take crucible for the last 24 hours as an example I've seen more red death as a primary than any other weapon. It's good when people have different weapons. It sucks that some people (like myself) may never get certain weapons but it would assure that most people are using a variety of weapons instead of 1.