The community of Area 51 cannot answer whether the Music Fans site should expand the scope of their site. That question should be asked in their meta support (which looks like they already did).
The provisions for radically expanding a site's title and scope are to first see if there is a very compelling argument and and even stronger consensus to see if it's a good match, then make the case to the Community Team starting with the 'contact us' link at the bottom of the site.
On a personal note, I don't see this as a good match between potential communities. I am not going to interfere with that discussion, but there is not an intrinsic overlap in expertise and interests between music fans and dancers. Music Fans is about consuming and appreciating an end product where a site about "dance" would predominantly come from folks being dancers themselves. I can't help but draw a correlation in combining our "Travel" site with those of "Vehicles" and "Aviation" based on an "almost all dance is done to music" premise. You can see the contextual flaw in that thinking. My daughter (ballet, tap, jazz, and lyrical) would likely want to ask about her studies and technique, but the top tags in Music Fans are [identify-this-song] they heard on some television show or commercial, and what the lyrics are to their favorite song.
Different audiences; different goals and interests.
… but that is outside the scope of this site.
