From what Joe and Matthew both said in their Meet the Teams, they seem to be up against audio engine performance limits now, so I think they'll have to be somewhat careful in just adding stuff, or at least use baked-in effects when adding effects so as not to overload the worst-performing systems and causing audio crackle and stutter. I guess they could produce Busy, Sparse and Uninhabited variants of their existing ambience assets and blend those together with the local emitters.
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I'd like the difference between Sol and an unexplored system on the rim to be very jarring. When in an empty, unpopulated system you'd start hearing ship sounds (internal modules, hydraulic/fuel noises perhaps, vibrations/groaning from the internal structure when accelerating/decelerating/turning etc.) which you wouldn't normally hear. When in - say - Sol, you wouldn't hear any of these with all the noise from passing ships, radio transmissions etc.
That might help some if performance is an issue - you could cut out a lot of the normal, low-volume background sounds since they wouldn't be heard anyway.
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Oh, one other sound I'd like which'd be quite useful - when the reservoir is emptied and refilled from the main tank, I'd love if you could hear the fuel transfer (glug..glug... I don't really want to know what you'd use for inspiration for that sound ). It's important to know when it's happening.
I know there's a "Main fuel tank drained", though that seems to play at random times, in my experience.
Audio detail or feature, hmm not sure, but I definitely would love to see more musical tracks in the playlist. Game feels like it needs more music variety.
Thanks for all the hard work!!