Anyone who knows the answer is likely busy composing, so I’m just speculating. The current trend of fusing disparate genres will continue, perhaps to the point where a set of rules for doing it well will be codified (and then those can be broken).
Additionally, while there’s been some work on using studio tricks to record pieces that are too complex for an individual band to play, no one has taken that to the logical progression of recording pieces that are too complex for any group of humans to play. The 40 piece orchestra can do many things, but the 40,000 piece orchestra can do even more.
Well, in my humble opinion, the rules are descriptive, not prescriptive. Later music may be composed to conform to an earlier composer’s rules - and that’s pretty much the basis of most conservatory/university courses in composition and theory - but it doesn’t have to be that way.
Famous story about Debussy - one of his composition professors complained that he was not following the rules, and Debussy’s response was “I follow no rules - only my pleasure.” to which the prof. replied “That’s fine, provided you’re a genius.” I’m desperately looking for a cite, but my bookshelf and my google fu are failing me.
Some composers prefer (or downright need) to have rules to work within, or around. I’m especially thinking of Schönberg here, and how Serialism was for him a solution to the problem of Pantonality. With so many possibilities open, Schönberg found it overwhelming to compose. Serialism appealed to his sense of order.
So, as far as I’m concerned, make up your own rules or lack of rules, and leave it to some musicologist in the next century to write a thesis on what you were up to. The musicologists need something to argue about anyway.