If the next Bethesda game launches broken while having premium mods available, my cyncisim will ascend to Super Saiyan.
There will always be someone out there wanting to make a name for themselves or wanting to undercut the next person.
A game fix that is trivial, will almost assuredly be dragged down to being free, since no one will pay for something that someone else is will to put out there at no cost - and that person gets the recognition / following.
When it comes to larger and more intricate mods, things that actually include their own assets and properties, perhaps are regularly evolving modes / maps etc, are far less likely to be free when the author puts them up at a price. You essentially have the choice of piracy outside (with the same downsides and upsides as usual) or their price on the workshop.
The assumption is that the market will force people to charge the appropriate amount for the better sales / content, and competition will push pricing in the right directions. Free content will always be there and be produced by someone, and likely be the most popular. However there will likely be larger projects that gain popularity overtime, that are paid for.
If it goes like that, it will be exciting, but the next months will be crap as the market goes all over the place. With no curation and pricing structure from Valve or Bethesda, it will take time for things to settle down
I applaud this practice. We have considered selling our HL2VR mod eventually. I love companies which enable people to actually monetize their work. This is terrific for content creators.
And this is an example of something I would buy - at the right price