Just to add a little to what I wrote above--although as I wrote, I don't think the BIAB concept could ever go as far with classical music as it has with jazz, pop, folk, etc., I agree that it could do more than it has so far.

For instance, there are already several classical styles. Why not make RealTracks that go with those styles? That should be possible, and would be nice.

Of course, if that would mean hiring a full symphony orchestra to record phrases for the RealTracks, that could get expensive, but of course they do that for sample libraries. (I assume one could save money by using lesser known (while still good) orchestras, rather than going for the New York, London, or Vienna Philharmonics!) And of course some tracks could be recorded by soloists and smaller ensembles as well.