Are you prepared for the incoming wave of DMCA takedown requests if this proves to be popular?
If someone spends the time to create content for this platform, how can they be sure that it won't shut down next week?
Can players create private content, such as for a D&D campaign?
If a player starts using content created by someone else, and it gets taken down for either copyright or because the author removed it, can that player continue to use that content?
In fact, can an author remove content at all?
Is there a system in place where the legitimate owner of an IP can create content for this platform and monetize it in some way? Tabletop Simulator may be a den of piracy[0] but there are some games for sale there as well: https://www.tabletopsimulator.com/games
[0]: Ignoring that some number of users own the physical game and are merely playing with friends who are not in the area. Legally it might be piracy (IANAL), but ethically there's some discussion to be had there.