Seems that I will actively mentor again in this Google Summer of Code (as opposed to just review the submissions from students and/or acting as a fall-back mentor).
The project I will mentor is the “Make optional kernel subsystems register themselves via sysctl”-one from the FreeBSD ideas page.
The student already got into contact with me and it looks like he is motivated (he is already subscribed to several FreeBSD mailinglists, which is not a requirement we have in our GSoC docs).