Thanks a lot for your offer, we would be of course very happy to welcome new
contributors, would they be for a short time or longer term...
For me it's a pleasure and honour to contribute to free software movement and richness with students :)
Regarding mentoring, I think I begin to have a rather precise idea of where to
find any part of the code, even if I haven't been deep into how every function
works... As I live in France, there is no time shift, voice calls are free,
but my Spanish is very very basic, can't count on that.
The main problem is that I'm very busy at work in July (finalizing a telecom
circuit!), and in family holidays in August, but one week in Randa (focused on
our topic). Answer to questions may take several days.
Don't worry, it will be just two or three indications in email format, and that can be in septembre or october, and just if the students need it.
I think it is more rewarding and motivating for newcomers to add small new
functionalities rather than understanding broken code. In our mantis tracker
we have several ideas, for example:
#1347: mute all but selected track
#3298: duplicate Title Clip
#2513: Disable all effects in Timeline
and I have others in mind:
-properly handle constant quality encoding (tiny UI change)
-make transition/effects selector more visual (icons/animations)
-copy/paste between projects (I have a dirty beginning partly working)
I completely agree with your point of view regarding motivation.
Indeed, I've not commented for now, but they are very interested in contributing with something related to UIs.

Once got in with little tasks like those (which can take some time for
beginner), it can be time to settle on more advanced work, "level 2", still
rather visible:
-re-enable movit (in GL monitor)
-re-enable ports to OSX, Windows (many changes since the last time it worked)
-implement cross fades on a single track (a la shotcut)
-hunt easy bugs
-fix static analyzers warnings (I already made most of the work with cppcheck,
scan-build and krazy) and look at valgrind messages
Great plan and roadmap.

If your student would prefer things more related to signal processing or
multimedia framework, then it might be better to look inside MLT, movit or
ffmpeg/libav. Things I would love (don't know what these projects have in
-enable hardware encoding (as we can now have most processing in GPU)
-call graphics filters from GMIC & other still image programs?

Hope this motivates people ;-)
With all of these ideas and proposals, I have much more than enough for my meeting with students on next week, I hope they will keep hard with this and not only just for passing the "must" of the university.

Thanks a lot to these list, developers, not ony for these messages, but also for your fantastic work ready for so much people all over the world ;)