I wonder whether modrana will ever become a good alternative to ovi maps, sygic and navit taken together.

Seriously, sygic and ovi maps are closed-source, and navit cannot show satellite tiles.

Though, I think that HTML/XML/XUL are better than Python.

And for me the main feature is being able to use it off-line with limited battery.

I would be glad to have accelerometer/gyroscope/compass combination precise enough to replace GPS when its signal cannot be received (Underground?).

For now, Modrana is my favourite, and Sygic is the antipode.

Agree. For these cellular providers, even infinitely large credit would hardly be enough.

An idea: put a barcode scanner on a lamppost; when it reads appropriate barcode, it activates WiFi router for several minutes for the person who gave the barcode to get anything it wanted.
Potentially, the camera could track barcode movement and rotate WiFi router's antenna correspondingly. It would make WiFi harder to intercept, power-saving, and the whole system could get electricity from a solar panel and use the same camera which is already used for other purpose (like, traffic camera; and then passengers could have Internet on the road).

Who will pay for WiFi (free WiFi is quite rare)? Well, if you already have Internet from XYZ at home, then make barcode from text "XYZ", and cameras which have XYZ's WiFi routers will then connect with your device and log into XYZ's service. You would use the same Internet provider as at home, you wouldn't need to worry about slow-and-expensive cellular data plan, and, as special benefit for XYZ, its routers would not need to work all-the-day: they would be activated only when camera reads the barcode, the electricity would be from solar panel, the solar panels would be connected into a grid, and XYZ could claim itself to be "green". The electric radiation pollution wouldn't be too high (compare pointed beam with omnidirectional waves), the interference would be reduced, etc.