I don’t think a photograph/image repository special to MusicBrainz is the path forward, but I could definitely see the use case for a general purpose libre/free-as-in-freedom artist image repository. Maybe something @KodeStar would want to be involved with? (@KodeStar is the guy behind https://fanart.tv/) It wouldn’t exactly fall under the current scope of FanArt.tv (which is a bit in a legal grey area), but I think that’d be the current project that I know of that I can see take this up with the least resistance.
That’s cute. The work will never be finished. There will always be new artists to track down and add photos for and there will always be artists that are so obscure that no photo will even be found for them. Just like MusicBrainz itself will always be incomplete, so would such a project.
Note that that doesn’t mean that we/you shouldn’t strive towards being as complete as possible, just that I don’t want anyone to have the illusion that actual completion is actually achievable.