That is a great idea but the scanner would have to revamped or a new model unless they could push the data through the serial cable.
Yes, they could not do it with an existing scanner.
It does not need to be a touchscreen display.
Many of Unidens scanners have awful displays, going back to the 396 with that freaking blue that you could not even see the text, plus it hurts your eyes (many people are sensitive to LED blue).
Use that display, put knobs on it with a resume button, and make it the remote head for a desktop scanner. You could use it in your car, or have the scanner in some position away from your desk. Hell, it could even remote over wifi or bluetooth (although that would probably create a problem with the car trying to connect to it).
But the point is, the desktop scanners with metal bodies do work better in cars in my opinion, and if you can mount it away from the dash with the engine RFI, and now the RFI from all the fancy electronics in the nav system, so much the better.
But a remote with a display you can actually read in the car, awesome. It would be a best seller, if the receive is at least as good as a 996XT