I would like to see more customization available for the main navigation screen.
To that end, I would suggest a modular approach to the screen.

eg: Have selectable modules for speed, compass, altitude, speed limit (really wish this was available in the USA), eta, miles remaining, alerts, etc.

Then give the user the ability to choose what modules they want to see, where they want them on the screen, and possibly choose from various visual styles for each module.

If it were possible for users to create custom modules (aka plug-ins), that would be even better.