Re: #2: For what it's worth, GPSD uses an HTTP protocol, so you can very easily host a GPSD server on a remotely accessible location and use Maemo Mapper to use the internet to get GPS data from that GPSD server. This functionality is already built into Maemo Mapper. Of course, Maemo Mapper only plots a single GPS location on its display.

If you treated GPS clients as "POI", however, then Maemo Mapper can display an arbitrary number of GPS positions. All you'd have to do is write a little application that runs in the background (separate from Maemo Mapper) that collects GPS information from multiple sources and updates Maemo Mapper's POI database to reflect any changes. With each update (or block of updates), you can use Maemo Mapper's DBUS interface to force it to refresh the screen (thus updating the drawn POI locations).

If you wanted, you could even provide a custom POI icon that looks exactly the same as the blue dot that Maemo Mapper draws on the screen for your current GPS location.