As the mostly missing-in-action maintainer of CoreBase, I am very excited to hear a GSoC student interested in GNUstep. I started CoreBase exactly because it was mentioned many time on this list as a pre-requisite for a WebKit port, so it's really good to hear someone willing to put the time in.
If you haven't had a chance to look at the CoreBase code, yet, I can tell you it's been sitting for the last 2 years with little-to-no commits. That being said, I would be glad to help point you in the right direction anyway I can. Despite my lack of participation recently, I still keep a fairly comprehensive to-do list. I'll do my best to support you in any way I can.