Music has been developed extensively over multiple centuries which has increased its diversity. For example, tonality was established, atonality was emancipated.
Atonality is just a combination of plain laziness in the face of complexity, a refusal to take an interpretative stand, simply the result of using a non-viable audiation method for difficult music, and/or a limited theoretical approach (Oh, where are the chord progressions and cadences! Guess it's "atonal"!).
Are you saying it's the laziness and/or limited theoretical approach of the composer or of the person doing an analysis of the music?If you are saying it's the person doing the analysis, does that mean that atonality doesn't actually exist?If you are saying it's the composer, I'm honestly not sure that any of what you said makes sense when you look at the first explorations of atonal music (e.g. Liszt's 'Bagatelle Sans Tonalité') and why early 20th composers started to head in that direction.
Tonality is fundamentally an aesthetic, mental procedure that has levels of skill. Atonality, doesn't really exist as a "property" of music. You'll often find that composers who write music normally given this description, not being fond of the term.
"Dissonance" was emancipated. Atonality is just a combination of plain laziness in the face of complexity, a refusal to take an interpretative stand, simply the result of using a non-viable audiation method for difficult music, and/or a limited theoretical approach (Oh, where are the chord progressions and cadences! Guess it's "atonal"!).
We could develop synthetic chords and scales. Scriabin famously created his Prometheus chord by altering the whole tone scale. In terms of creating a new genre, music has already become very fragmented so new genres may be likened to or included within existing genres. Therefore, it is quite difficult to create music that is truly innovative nowadays. Polychromaticism is probably the first step towards achieving this in the 21st century
I don't think polystylism is the mainstream musical trend of the 21st century.
The fact that game and film soundtracks (sometimes) use many styles of music is more a result of the production process. Film and game composers aren't given total freedom over what they do. Often the director or producers will say "we want music that sounds like this in this scene" and it's up to the composer to write the music they want. So I don't think you can look to films and games to see what future trends are for music in general, and certainly not for the concert stage. If there is a trend in 21st C. music I'd say it is closer to individualism, where each composer tries to develop their own musical style/language, unique from everyone else's.
I couldn't begin to guess where music will go in the coming centuries