The present genre most likely to survive as classical works have done is in metal.
It's an exaggeration when people point out how classical works were for 60 instruments, or even a thousand. Those instruments were playing in unison, and there were only at the most five distinct melodies at any given time.
Now bands have about four or five instruments. Sometimes their interaction with eac other is pretty straightforward as we see in pop music and other times there is an application of counterpoint just like in classical works.
We also have to consider technologies, because a synth can sound like an orchestra on its own.
Mozart and co. remain pioneers because they did it best in their time, and no one's ever composed as they did. But with the variety of music that's out there now, it's most likely that stuff comes out more impacting even though not as 'intelligent' as these old works.
Honestly though, how many people nowadays are fans of Mozart the same way there are fans of Symphony X? Because even if someone likes Mozart, oftentimes this is just a casual thing, and they point out some piece that came out from the movie 'Amadeus.' So even nowadays, the true Mozart clique is very limited. I know I'm part of it, I don't know about others.
Another point. There has also been a significant shift from composing, to songwriting. Things are simpler nowadays because there's no need to complicate things. And there are songwriting masters who will eventually be mentioned in the same league as the compositional masters. I think that list will include people like Lennon, Michael Romeo (whose lead performance is secondary), Mustaine and Billy Joel.
I know I'm saying a lot, but the main point is that stuff that comes out today has the potential to be more impacting than these works of old, and it is my belief that natural selection will weed out the shit of today, leaving behind several works, most of which are in the metal and perhaps jazz (which I don't care for much) genres.