There is a former maxis employee doing exactly that for high quality building mods in cities :skyline. Its working well for him, but that has partly to do with the his former job, the pure quality of his work, and the press attention hes garnered. I suspect it was the timing of maxis closing and Cities releasing that helped the most, although his models are excellent in every way. Its just that even with great art, without some attention you will languish.

It would be a great thing if Valve implemented a Patreon model for modding instead of direct pay. That would let people get the attention their great work deserves, streamline donations, and not change the nature of the modding community in the process.

Yes, to use your slightly off description. But there's nothing wrong with that if the people offering the money understand what the expectations are before donating.