Yeah, I mentioned that in original post, I think. Well, first problem is way to upload assets into the game, which someone said may be possible with third-party add-ons. Hoping a guru could sort that piece out.
I don’t have polished answer to your question, but the main thing is that the uploaded materials are created by the uploader and exchanged with the recipient. So, all materials uploaded must be original materials created within the ecosystems of the game. Then, it would have a limited-use license to be sold between players in the game. So, clearly, anyone who violates that would get the boot. But as far as auto-detecting that, that would be some guru work–am sure some less-than-failproof frameworks already exist. It would be impossible to prevent entirely, but my belief is that it can be managed. Unless people try to do it en masse, then the game would become unviable.
Please appreciate that the abstract concept of “exploitation” is one of those failed ideologies we need to let go of. It’s the idea that my individual gaming of the system to “win” is a win. That is an illusion. It is actually a global loss because it adds unproductive bureaucracy onto everyone’s backs as a burden we then must all bear to prevent it in the future. This is something that will be encoded in the game. People are enriched by helping others succeed and impoverished by attempts to exploit.