[...]
So: As it stands, enhancing geanyprj seems like it could be decent approach. Or forking it, since it's overview makes it sound as if its purpose is to dip into lots of projects/codebases, rather than enable good organization of a single project (and context changes, if opened in a different base directory)
Hope this makes sense Martin :-)
PS: But doing this in Python is a lot more appealing than C... But I can see the packaging issues may outweigh the convenience.
If you don't use one of the existing C plugins as a base, then don't let the questions over Python plugins put you off using it, you don't need to care until (if) you are ready to release it to the geany-plugins. Hopefully we will have gotten our ducks in a row by by that time :)
Also consider you could write plugins in Cython, which to my mind allows the best of both worlds, C and Python, and (untested) Python3. Or you can use C++ for plugins, or Vala.
So you now have too many choices :)
Cheers Lex