- Do you agree that from experience and observation, we can tell that certain genres or fields appear to become completed?
- Does this concept or another concept best explain what is happening?
(see e.g. Romantic-style piano. Google even did some really cool work in computer-generating original pieces that sound like that.)
The best results in computer-generated romantic piano music are actually not from Google but from an unaffiliated researcher - see Composing music with recurrent neural networks. It's true that Google Brain has released some generated piano sounds from their WaveNet, but those (1) are not actual piano sounds, rather they're the network's "dream" of what a piano might sound like; a real piano could never sound like that; also (2) these samples have comparatively little long-term structure, as a natural outcome of working on audio data as opposed to notated music.
These results are actually the reason I don't buy that "strategies we use to search for musical ideas without having to solve any NP-complete problems have dried up". Neural net inference doesn't do any NP problem search, and this network creates rather innovative music simply by virtue of successful generalization, enabled by some very good (I'd even say outstanding) features of the model design.
That music doesn't sound "rather innovative" to me. It sounds stereotyped, boring, and inept. (For the avoidance of doubt, it is also very impressive to make a computer generate music that isn't a lot more stereotyped, boring and inept than that, and I would not be astonished to see this approach yielding markedly better music in the future.) It seems to me like it falls a long way short of, e.g., the music of "Emily Howell".