I guess the vast majority of those games are non-free. And I think this reflects a lost opportunity to educate all those enthusiastic game developers about software freedom. It would be interesting to try to come up with a list of contacts of all those developers, find out what they're doing nowadays, perhaps engage into conversations with them to raise the issue of software freedom (and code-licensing for their fan-games). But that would need to be carefully coordinated to increase the chances of success.
If the ScummVM developers care about software freedom, then maybe this is a matter that should be raised in the project issue tracker (or any other means of contacting the dev team). Perhaps the ScummVM project maintainers themselves would like the idea of coordinating an official campaign to encourage free licensing on fan-games created by their users.
Is there any ScummVM developer here in this conversation? Or do we still need to reach out to them?