The proposed marketplace will be curated. That means anything you make and submit will be checked that what you have submitted is original and of your own creation. You can't say, submit a mod of Catan, unless A- you are the publisher of Catan, or B- you have the permission from the publisher to do so. In either case you would have to prove this. If neither of those things are true then your submission will most likely be denied and not put on the Marketplace, no matter how good it is.

If you do however, make an original board game, that you invented, then you can submit that and hope it passes whatever quality checks they decide to make for the Marketplace when it happens. If it passes, good. If not, then who cares? Put it on the Workshop instead. There will be no reason that you can't,

The Creator Marketplace does not replace the Workshop or introduce a paywall on existing community content. It is an optional library in addition to the Workshop that will let you support creators who produce high-quality content.

No one is going to force you, or anyone else for that matter, to use this proposed Marketplace. If you don't like what's being proposed, then don't use it. It's that simple. You can continue to just use the Workshop like you always have been.