I wish they'd just remove materials completely and tie it all to experience. Legendary/Exotic could require a ridiculous amount of experience to upgrade, but then we could earn it any way we choose instead of having to keep track of 10 currencies.

Better to eliminate weapon upgrading all together in the current fashion.

If you HAVE to have them, they should work similarly to how you get your character abilities. The upgrades should also be interesting things. No increased damage, increased stability, etc. The abilities should change the way you use the gun.

Let's say you have the icebreaker, and one choice for ability is what it has now. Perhaps another would massively increase the impact, yet only permit one round in the chamber and have huge reload times. So with that, there would be situations where you'd want a massive amount of initial damage at the expense of sustained damage.

Something like that. But having to level your gun up to do more damage is the laziest, stupidest, and most uninteresting and unimaginative mechanic.

An acceptable alternative would be to remove materials all together, yet keep ascendants, and require the gun's signature abilities ("perks") to be unlocked with materials. Damage upgrades, ballistics, and sights should be glimmer only.