Well, likely I'd be that mentor (already talked about it with vdvsx, our GSoC coordinator).
More like stabilization to be interesting to 3rd party developers (not much fun in developing for a moving API).
Correct (except for the buttons, we don't have those yet , and the mapping application - location stuff is supported by system libs).
So, as said, the thinnest segment is the GUI, but based on the feedback from this thread there is no such thing as too many possible triggers or actions