So I don't think it's fair to say that no-one is interested.

Ok, nobody is interested enough to actually implement this.

Another point to consider is that this functionality could conceivably be a step on the path to the full routing navigation that many want. Even if most or all of the code developed on this step needed to be discarded and re-written...

Ehh, the code is already there, take empan for the display an image on the screen part and mix in the stuff from gpsapp that talks to the GPS. You can even use the built-in imagepan visual or empan for mockups to visualize how such a display would work before implementing anything. But it doesn't provide anything useful for doing full routing on the empeg.

You need vector data to do routing. And it is not hard to use that same vector data to draw a map, or give you the coordinates of a an address/zipcode. Technically the route display in gpsapp already draws 2 lines out of such a vector dataset, the route we're following and the track that we've driven. A scrolling image doesn't help in either of these two areas and as such is not interesting in my opinion.