Here's the idea:
The community of developers build a basic, highly moddable game which will function as market place for that kind of game (a bit like dota2 or team fortess 2 is). Then those artists who make assets can sell them giving back a share back to the team who's updating the "game".

world case scenario: let's say a group of people build a racing simulator with one nascar-like track (or a simple cc0 one) and another bunch of simple cc0 cars. The physic and mechanics would very basic at first since the biggest workload should be made to make it functional (almost bug free) and extremely moddable with other cars and tracks.

The game itself should set some firm rules/standard to get things working: for example racing cars should always contain some strict requisite such rigging (wheels tires and, if cockpit available, also steering wheel) a minimal amount of lod (at last three: far away/ mid range and highpoly for player driver and/or when in ultra settings graphics). Optional things can be destructible parts (this can be detailed as much the 3d modeller wants) etc.

Additional tracks will also follow similar rules (these are expected to be more expensive since can be very complicated with LOD, animations and stuff)

The starting point for the generation of the basic game would be a Game Jam; and as for editor of choice.. Godot is the best guess. Since it's MIT licensed there are basically no licensing issues on what/which/who you should pay share. Also Godot philosophy for "node based" makes it perfectly suitable for make moddable games. The storefront would be, of course, itch.io and... maybe in future being integrated in itch.io desktop app?

Sounds like an interesting idea but probably difficult to make work. In order to attract artists and creators to make content for the game so sell they'd have to be confident that the game will actually have enough players for there to be people buying stuff. In order to attract players you'll need a game that is reasonably polished and fun. I suppose if you had some people bootstrap the assets for the initial game it could work.

Well, sometime ago some people would say that also the concept of itch.io would be probably difficult to work :P and, indeed, it was.

So, thinking it's worth to give it a shoot, I am currently trying to gather interest around this idea.

I've posted a thread on /r/pcgaming which it's the best place to try to make some noise (if people is up to) Take-Two initiative to crap around their loyal modders could give a bit of help... if this thread will manage to get a bit more visibility.

I've also pinged the Godot community here.