But how much prog rock, punk, psychedelic, EDM, trance, actually made much of a dent in the charts? Sure there were pockets of success, but insofar as popular music's concerned, I'm not sure those pockets were ever big enough to mean much in the big popular music picture.
There will always be cycles, but my guess is they will happen outside of the pop charts, although the marketing types will simply market their products (i.e. those pretty young things lip synching to the computer generated magic) to maximise revenue from whatever cycle and demographic is most lucrative.
In a way it's no different to what's always happened. Going back to punk. I recall the punk ethos, and the wonderful idea that anyone could do it, and I recall going to see many a rough old band that only knew three chords (or at least one barre chord shape) and were out there gigging in phlegm-flying rooms, and the fans wore all manner of wild home-made clothes and hair styles... and yet within months there were punk clothes available in department stores and bands with record deals that were marketed as punk but by golly they could play and were every bit as good as those that had existed before punk and even bands that themselves (probably wouldn't have described themselves as being punk) were marketed as such just to ride the wave and get in the charts.
What we need to pin our hopes on is the future of non-popular music. With the amount of routes to market available now, I think that's where the real magical stuff will happen and the wonderful music will be available.