I would like the ability to keep a pattern playing whilst modifying the drum pattern, or another section real-time, and then having those changes effect the current audio at the user's will. It seems this would entail improvements to the sections/playlist functionality.
Sounds like fun, but would it be worth the effort? "At the user's will" does, I think, give away what the problem would be: SOMEONE does indeed have to decide! The trick would be for the system to know reliably which version to play at any given moment, while changes were being made on the fly. Personally, I think a composing-oriented system should NOT be so fluid. Better to be sure that what is played will be just what you specified; then (after saving that version) make your changes, audition those specific changes as often as you need to, and only then register further changes if desired. A composer has to learn eventually how things will sound BEFORE hearing them played. Adjusting to ongoing changes while playing in real time seems to require too much smarts on the part of the system, not enough from the composer.
The only window that I could see being a floater is the transport.
A major advantage of floating windows is that they release maximum screen real estate for the composition itself. A stable interface with everything in easy reach is always nice to have. But the more you box in the notation grid with other permanent fixtures, the less room there is likely to be to view the part of the composition you are currently working on. So here as elsewhere, there's tradeoffs to be made...