I've done 600 miles of driving in 2 days. That's a great deal, especially for me. I wedge my GPS (hand-held unit) up on the dash under the windshield. It gives me my Speed, ETA to waypoints (I set at intersections of major highways so i dont drivepast them day dreaming) as well as a mile-to-waypoint readout. It also gives me fun stuff like heading, vertical velocity (ft/min) etc. Then I looked at my radar detector and I lightbulb went off.
Why not combine a GPS puck and a radar detector. USB it. I know it's a bit of work, but to have a built in radar detector that mutes music to alart you. And a GPS that mutes your music and lets you know your 2 miles to an exit, or aturn or whatever.
GPS will work under most windshields. If it doesn't look like a radar detector maybe the VA cops wont kill me. Ok, and since your at this, toss an FM antenna in it and poof, and all-in-one MMC custom dash-puck.
Just a thought. I thought it was a good one, but I had been driving a while. But if it interfaced with MMC right, you could offer it along with your software for retail.