How about an addition to Hijack(?), to use the microphone input
to monitor the background noise level in the car, and adjust the volume level accordingly.

This would be a really usefull feature, and it is something
that many in car audio systems already do.

Is this a possibility?

This has been previously discuss and I think the general thought was it wouldnt work very well. Most stereo adjust the volume based on speed not actual ambient noise. Maybe if we can get the OBD-2 stuff worked out we can implement such a feature.

my stock amp had a neat feature where it would make the stereo louder when you lowered the top (convertible). I wonder if that would be possible with the empeg too

one thing that I'd really like to see would be to store volume adjustments for songs. So when song A comes on, it automatically raises the volume 2dB, but when song B comes on, it lowers it 1dB.

I haven't bothered to figure out if it's doable yet, but something based on use of ID3 RVA2 tags would be useful: calculate mean amplitude of your collection, use RVA2 tags to adjust mean track amplitude to match.

One of these days I'll get 5 spare minutes and figure out why it won't work

Should be possible using the Phone Mute line tied to a sensor for top up/down.
As it is people use it to switch to/from AUX IN when the phone's in use, routing the phone audio into the empeg - it should be possible to make it raise/lower the volume instead...

/Michael