Matt,
"But what would you rather PG Music works on?"

Step approach. From my memory Peter G. mentioned that direct read from disk is being looked at for 2024. From what I understand, that supposedly will allow for near instant playback. If that comes to fruition and it works well, that would be a first major step toward live arranger functions.
Even if it will not be as fast as needed for arranger (direct disk read), it will still be an amazing addition, as it will reduce generation times significantly, so all users will benefit.

To give an example. It takes me an average of 6-7 hours to sketch out bones for song in BIAB (finding proper track, song parts, chords, automation, MIDI, partial regeneration etc.) With instant/near instant generation, it will reduce this process to 3-4 hours.