Payment can certainly enable mods to exist that would otherwise not exist; and Bethesda's input can certainly make some mods better, especially quest/worldspace mods that always feel slightly out of place.

But right now, that is not what they are doing. They invited mostly authors who make items or other small content that would be made regardless; mod teams are excluded; and if the rumour that all CC mods must be .esl files is true, they are capped at 4000 records. Bethesda's contribution to smaller mods like this is minimal, but they take all of the profit while the author gets a lump sum. The biggest ticket creation we can expect is one of Trainwiz's quest mods.

This opens them up to entirely avoidable accusations of nickel and diming.

I really, really hope Bethesda will focus more on big projects. I don't know the FO4 scene, but worldspace mods like Beyond Skyrim would benefit massively. These are the projects most likely to fail due to time and money constraints (Rise of Mannimarco) or sacrifice quality to meet a deadline (Falskaar).