Rock history is full of them
you got the mid-sixties, everything swirling around together, experimental and weird or exotic influences (raga, etc) coming in but it's still dance music in some sense and still pop (jimi hendrix first album nearly every song is about 3 or 4 minutes)
then that splits into the progressive direction (very long tracks, undanceable, etc) versus the 2-minute bubblegum pop (which then becomes glam).
the overly brainy versus the merely physical / sentimental. FM radio versus AM radio.
and then another moment is punk / early postpunk, where loads of ideas and impulses are swirling but still contained within pretty direct and visceral and focused music (e.g. the first Joy Division album, which is essentially a hard rock album with weird sonic hollows in it)
but then the centrifugal syndrome sends the various elements off into their own directions - industrial, Goth, synthpop etc - more defined genres but much narrower
going with your coalition metaphor, or the idea of political parties that contain different populations, classes, interest groups, regional groups, etc, so that they are effectively coalitions
the coalition-moment in rock history are the ones where the music is able to dominate the pop mainstream - like a political party winning a landslide election.
1965-68 you have records like 'Strawberry Fields Forever' and artists like Hendrix actually in the pop charts - because the experimental impulses are contained within the focused economy of the pop single
then all that becomes what they called the Underground - progressive music - like an opposition party that can't speak the language of the masses