I wouldn't take a lack of example questions to mean that the site is only supposed to be about modern popular music. I would really value enthusiasts' perspectives on all forms of music, as they're the ones who discover the beautiful details that give classical and operatic music its staying power.
It's probably true that the majority of this site's users will be interested in music that is currently popular. That might even be a tautology: popular music is popular. Still, users who are interested in particular genres, eras, media, etc. can use tags to filter for questions and answers about them. This is one of the best features of the Stack Exchange engine, and it will certainly be important here.
It's also true that many (probably all) expert music fans are also musicians themselves, and there are tons of musicology questions on the Music Practice and Performance site. If this site graduates to a full release, perhaps some of those questions would be migrated here, as I feel this site's title and description makes it a better fit for questions about the history and meaning of music. That would free up Practice and Performance to focus on the finer details of performing and conducting operas and symphonies, while we can discuss, for example, the best movements and arias to get our kids interested in music.