You can already do that with Steam[0]. They allow publishers to generate keys for free. You could sell the keys on your own store and skip Steam's 30%(?) cut while reaping the benefits of their software delivery infrastructure. There's a fair use policy[1] involved, though.

[0] https://partner.steamgames.com/doc/features/keys

[1] https://partner.steamgames.com/doc/features/keys#3