I thought this too and I think that's a fun and valuable kind of goal to have.

So it is really a question of using characters that are not original? Is mosaic a world (or concept) borrowed from a media source with all original characters, or with original characters as the main/POV characters but allowing borrowed characters from the canon in minor roles?

Or, if we want to hardline ban Tony Stark but allow open source characters, there could be a new style or supply that specifies interaction with open source characters allowed, and mosaic cannot use borrowed characters at all.