u/Shaemis

This would give them some immediate short-term use after unlocking all weapons, and long-term use for after you unlock future skins. It would also permit you to slowly work on other guns you're not using, or to expedite the prestige process on ones you are.

Mostly it would just give fragments a current sink after your first dozen hours in the game.

At the moment, it's sort of pointless to interact with the anvil event after a while, same with wells since the downsides outweigh the chance for a little bit of gold or souls. Sometimes I can't even be bothered to chase around the loot goblin, I wish he just dropped a joker instead.

Doesn't have to be a ton of XP, anything would make it feel more worth hoarding them.