The one thing that I like about this concept (and correct me if I’m wrong) is a MMO sandbox testing playground of the products listed, but the incentive for artists is simply not there. I already get 70% royalties with my store at https://www.cgtrader.com/ with potential of 80% if I up my quantity and quality, cgtrader gets around half a million visitors a day also. These are already low poly AR VR and sometimes 3D printable objects in many cases are drag and drop into an engine of your choice - they even sell UASSETS (not even sure they can legally). I believe that the “edits” required on most assets are so specific to that game/project that the new product would be worthless to most others, I’ve bought many products and created these changes from LODs/lightmaps/retopo/rigging and even re-texturing and in some cases I’ve spent more time modifying than the original creator spent making it from scratch.
I remember taking on a project a while back where I was offered 25 bucks to make a realistic skin and hair material on an existing stylised character in the UE4 marketplace, unfortunately the hair was not even unwrapped and the person who made the offer refused to understand that and said no edits of the model should happen - said thanks for your time and relisted the job except only offered 15 bucks. But I digress, the point is that modding has immeasurable cost and very little use beyond what you’re modifying it for. The most popular assets are the most compatible ones in my experience.
I can imagine some issues with artists and assmods on your business model.
Imagine an artist creates a fully rigged/morphed/textured and optimised anatomically perfect character that’s taken months and an assmod comes along and profits off it simply by making the hair purple like a 5 minute photoshop job, I imagine the artist would not be pleased. Just as one example. CGTrader/ TurboSqud and Epic marketplace have policies regarding re-sale, however in your case artists would have to sign off on those rights of copyright protection and enter a grey area of complete reverse engineering to blatant theft. Will you have any policies regarding to what extent of modification is too little? will the base artist have any say to a modified product based off their work?