I am optimistic about the future of classical music, and music in general. There will always be a segment of the population that seeks out quality music, and will support it enough to sustain it, and that of future composers. For a fascinating read on this subject and related subjects, and to put this in a historical perspective, read this great article:
http://www.city-journal.org/2010/20_3_urb-classical-music.htmlNow, as far as "popular" music is concerned. Look at it this way: just how much lower in quality can it get? We now have a very popular form of "music" that is devoid of one of the previously essential ingredients of music: melody. We can argue about what exactly constitutes a good melody, but I think we can at least agree that it doesn't have to be traditional melody. BTW, if you like string quartets, and on the subjects of 20th century music that will stand the test of time and non-traditional melody, try the Bartok string quartets. Challenging music for sure, but brilliant and sure to stand the test of time.
I believe (hope?) that the time will come when the masses will be so starved for the kind of stimulation that only quality art can provide that many will return to the appreciation of quality music. I think that some of the points raised in the linked article point to this very real possibility. I also think that we should be careful about indulging in too much negativity and fatalism around this subject. If we truly care about the future of quality music, should we not take an even more active role in it's promotion and survival? At least by staying as open minded as possible when it comes to supporting music that may be challenging, and less safe and familiar, to our musical palettes. By not doing so we run the risk of letting our "preferences" become a kind of elitism that will do nothing to promote the creation of new quality music.
BTW, the Emerson Quartet's recording (DG) of the Bartok quartets is wonderful.