Interesting concept. What features do you expect to have?
Blue tooth or hands free are not very useful because you buried the mic.
GPS could be good
G-FORCE METER for sure but remember it would be biased by not being mounted at the centre of mass.
I dont know what ECU you are running but have you considered a CAN based gauge?
xrattiracer built himself a rather cool one here: http://www.msextra.com/forums/viewtopic.php?f=67&t=56565