I’m much less interested in half measures, whereby the public might be granted access
to scans only for, say, educational purposes, but be improperly prohibited from using
them commercially.
Those kinds of compromises undermine the public’s right to reuse public domain works
and can lead to people hesitating to use them in any way because they are unsure of
their rights and fear unknown punishments.
Whereas the licence on that Rosetta Stone scan by the British Museum is indeed "non commercial" only:
License: CC Attribution-NonCommercial-ShareAlikeCC