Welcome to Hurd!
I'm not sure what you consider a small task. Perhaps you could look at my March 9th email to this list, entitled "RFC: kernel trace facility". Briefly, I want to instrument the kernel so that we can trace the messages going to and from a particular task. Our current way of doing this (a program called rpctrace, that you should probably try out for yourself), leaves a lot to be desired. I think just about everyone on this list would agree on the need for such a facility, although its actual design is still open for debate.
Actual kernel coding is required, which is somewhat rare on this project, because with a microkernel architecture, so much of what we do is in user space.
I've started work on it and have a little bit of code written.
Does this look like the right size and complexity for you? If not, I'll try to suggest something else.
Thanks for your email, and for any help you can give us!