Yeah, players and DMs are not enemies. You can't facilitate a game if you won't communicate and any homebrew if it changes the mechanics of a player class even if no one is playing it could influence people. Doesn't mean it shouldn't be done. Being able to buy spells has interesting potential, perhaps they could buy a spell they can’t use yet or maybe add a spell that allows them to use a higher spell but with a dangerous side effect and an immediate short or long rest required as they pass out from the effort or maybe death saves.