As the title says, please let us spend some kind of materials/currency to reroll a weapon masterwork. I cannot count how many times I have received an otherwise perfect gun roll only to have it ruined by a reload speed masterwork. I would absolutely love to have the ability to spend some of my excess currency to reroll it until I get what I want. For guns that aren't able to be crafted, this feature should've been added when crafted guns were introduced in Witch Queen. This would also make Banshee a far more useful, valuable vendor for players of all levels and help keep non-crafted guns relevant.
The worst part is that it wouldn't even be a new feature. Bungie could quite literally copy-paste it from Destiny 1 because we used to be able to reroll Iron Banner weapons at Banshee in the prior game, too. In fact, it was the best kind of reroll because you could change what perks you get rather than just your masterwork. All it cost was some upgrade materials and Motes of Light.
[url=https://archive.ph/yrfgi]Here's an old D1 Planet Destiny article about it.[/url]