Actually bearing and distance to a waypoint can be enough if you know where you are going. Early GPS avionics were all alpha-numeric displays. Don't get me wrong, moving map displays are AWESOME.It is hard for me to imagine a useful GPS implementation that isn't superimposed on a map on a higher resolution display. Should be interesting.
Bigger issue is that it is only useful on the surface.
For military stealth applications, I Imagine them swimming a heading with the compass and popping up to check position occasionally.