Re: The use of the Ab6/9:
oooh that's a sexy little sound. You got me playing it now. And I think you are right in calling it an Ab6/9. See you back in the main thread.
Re: The use of the Ab6/9:
Hmmm, I'm thinking I'd start off with an octave based riff - warm, but clean. Then maybe establish a basic chord melody riff with variations before going into deep space.
Re: The use of the Ab6/9:
The G major and Ab Lydian dominant would sound cool over them. Just work your melody line to switch from one to the other as needed.
I'd be sure to focus on the phrasing, open space, and tone - octaves are also nice for that. If you play slow enough you can use the common tones of the two scales to bridge chord changes... lots to experiment with here.