With the new restrictions that mods can’t retroactively become paid mods, nor can they be dependent on others sounds fine on paper.
But consider what having this kind of system in place will do for future games and mods. I believe this will discourage collaboration and ultimately will cause a decline in quality. If paid mods can’t build off of others, then there would be less incentive or option to build integration of mods. Anyone remember mods like cobl, cm partners, and fcom for Oblivion? Those would be impossible with paid mods. And since most modders would (rightfully so) like to maximize their income, I reckon many would exclusively make their portfolio be paid mods, even with restrictions on what they can build.