I think we’re missing out by not having this as an option. Modding can provide a good stepping stone into full game development, and if people can earn money for their work, they can justify spending more time on it or potentially even doing it full time.

Yes. Those who don't want to monetize their work (which is actually respectable) would standout even more. In example there could be two versions, one free version and one paid version with a few little extras to support the developers. This is a way to handle paid software even in Open Source, in example on Android where such a payment system is integrated.

There is no need to have an account on a different platform, so I can support the developer, and another account for another platform that wants my bank accounts. I speak about patreon and and the likes. It's all here, with my Steam account and money from Steam.