Something has definitely changed in music (a few things) - at hockey games they are playing strictly rock up until 2000. Part of it is demographics, but there's just nothing to replace 'Welcome To The Jungle' by Guns and Roses that has enough widespread acclaim.
In other words: there's probably plenty of great stuff to replace/supplant 20th century hits, but unless you continually skulk random soundcloud pages you won't find it. All you get access to is undifferentiated pablum pop by default, which is amazingly less brave than it has ever been, musically.
The rest of music is very exploratory - production tricks, sounds, styles.
It seems that most basic melody and rhythm stuff is just to boring - but that is what sticks over the long haul.
So I think a lot of music today is too specific, and due to what big-pop is ... never sees the light of day anyhow.
We may in fact see a lot of 20-century music linger for a while.
That said, we don't listen to a lot of 1st half 20th century today ... though still tons from the 60's-80's. Top selling albums are consistently Queen, Metallica, Eagles.