Have started actual coding for GSoC this wednesday (start was 2 weeks delayed because of exams, which I'll catch up). Still just getting up to speed, but looking now into the PHP RDF framework ARC, whose RDF store will replace the currently used RAP store in Semantic Mediawiki. Usage ARC itself looks very straightforward. Just have to figure out the SMW Store API. Looking at the SMWRapStore2.php now, to get an idea.
If you want to follow my progress in (approximate) real-time, then see my twitter.