Yet another form of content segregation, just like restricting adult content to .xxx. It's one thing to add new top level domains, but it's quite different to give one to an organization (MuseDoma) which wants to promote "authentic and verified" information, according to their proposal to ICANN. The usefulness of domain names like this is directly proportional to the power handed over to the controlling organization to shape public discourse.

Notably, the definition of "museum" already excludes for-profit and virtual museums.