I'm ok with paying for mods, however there needs to be some sort of quality control and a good solution when it comes to hardware-related problems, compatibility issues with other mods, etc. because these things will happen.
Currently, if something doesn't work it's not really an issue but with a platform like that I'm not sure how they want to solve this without ripping off players.

It would be nice to have a fair system to reward modders. It's a lot of work. Then again, it will make modding more problematic because the moment money is involved copyright issues probably will arise to some extent.
It also could cause damage to the modding community by inviting profit oriented people flooding the community with mediocre content.

If Bethesda wants to do this right, they also should consider keeping the fees low, trying to pay for servers, etc. but I have this feeling this is just about to become another cash cow, trying to rake in as much profit as possible - and in the end most gamers might not even care if they are being screwed as long as they can consume some virtual stuff.