does your car stereo run linux?
It runs Linux (the kernel) it doesn't run a distribution like redhat etc...
built in microphone
It's not built in, there is a plug to take a microphone for later VR stuff...
free cpu power
It does have free cpu cycles, so more advanced audio codecs can be supported in the future...

You can do whatever you like with it, it just takes a bit of effort on your part...

Jazz
(List 112, Mk2 12 gig #40. Mk1 4 gig #30. Mk3 1.6 16v)