I'm not worried a whole lot. All this does is shorten a game's life. If I want to mod a game, I'll find free mods. If there aren't any free mods that do what I want, the game goes on the shelf for a few months or more while I play any of a hundred things I own but have yet to try. I love Skyrim but the free things I have now are more than enough.
Wait until these modders get a taste of reality. First, a lot of them are going to be shocked at how small their cut of the action is. Second, and probably most important, if people are going to pay for a mod they are going to expect it to work flawlessly the first time. They are going to be a lot less tolerant of excuses. When a patch comes down and breaks that mod, customers are going to expect that to be fixed in a matter of hours, not days or weeks. When a mod is released with any bugs, people who paid for it are going to latch onto those bugs like stink on shit and rate that mod into the ground. Give this system a couple months and no sane solo modder will charge for their work.
Huh? I'm sorry, I was thinking about cake.