I'm wondering how big the market would be for it. Most people who aren't FE nuts don't care that much about an MPG readout. Newer cars are starting to come with them and the ScanGauge does so much more than the MID when you look at all the sensors it reports and its diagnosis capability.
But, the MID is WAY more powerful than this thing:
http://www.porcine.com/gps/mpg/mpg.html
It's for aircraft, only reports instant mpg, requires a GPS to calculate speed, and costs $199!
SVOBoy: Yeah, we use metric, but I personally like US MPG. It's just a number that's easy to deal with. I don't like using Imperial MPG or the L/100 km measurements at all. However, I do like km/L so the MID is perfect in that regard.