Just a thought. If Open source GPS can overlay a new set of image tiles onto the GPS display, could it be used to display a scrolling set of route sheet prompts on the screen?
Does this make sense?
Instead of just displaying a standard trace over a map, could you have the screen switch at the defined turn point to display route sheet information?
Imagine being guided to your turn point and then seeing the promt, "turn left at pillar box". A nice fusion of trad audax-style navigation with all the security of map-based route finding.
For true usability, it should only display at a set zoom level and disappear at lower zoom levels.
Possible, or am I dreaming?