As a classical music aficionado, I really, really hope there will be a Classical music app!
The Music app is almost useless with classical music. I am usually either looking for a specific work or works by a specific composer. If I end up with several options, then I am interested in the conductor, orchestra, and recording year. None of this is supported by the app, as no one is interested in knowing who’s the composer in popular music.
Also, the simplistic view of music as separate pieces does not work with classical music. If you take a concerto or a sonata, there are several movements (often named after their tempos, e.g. largo, allegro, adagio, andante, presto, etc.). Large operas have dozens of arias, recitatives, and choruses.
I am an Apple Music subscriber, but very often I find myself listening to music from other sources, even YouTube, as either Apple’s library is very small, or the search functionality is hopeless.