True. It would be quite a can of worms to cover every copyright and trademark in existence. So, how about just copyrights and trademarks that are known to an average person. That seems to me like it would be easy to implement. The marketplace could simply publish a list of generally know copyrights and trademarks and simply require product developers to submit proof of license to sell if they are going to try to sell anything on the list.
On the other hand, there could be rights holders to well known copyrights and trademarks who don't care at all or maybe even encourage unlicensed distribution. Like
Skyrim pendants for example. They are being sold everywhere! If I were the rights holder I could single-handedly send C&D orders to each of those marketplaces and it would take me all of a few hours. So, perhaps the rights holders look at it as a form of free advertising. Or maybe they just don't care, sort of like how most farmers don't care if people in the community stop their car and jump out and grab an apple or two from one of their orchards.
Also, a year or so ago I contacted Lucas Arts in an attempt to get a license and they said no. However, they didn't say selling a product related to their brands was strictly prohibited, they simply said that it would be quote, "inappropriate." I tried to get them to clarify, but there was no reply. It was almost as if there is a sort of unsaid aspect about it that they were hinting at, but at the same didn't want to get into details about.
I have a Star Trek pendant that a client recently asked me to make for them. I could easily put that up for sale, but before I do that, I'm going to contact the rights holder and see what they have to say about it. I wonder what they'll have to say.