I, for one, do not expect anything new from GDC, on the SCE front. They might show some real time stuff from some of tehir project, yes, but I wouldn't expect full blown trailers and such, let alone trailers for unannounced games.
They might do some PR, though, but I won't be counting on it, nor would I expect something important, to the gaming press, to be presented.
Yeah... I doubt GDC is a good platform for doing consumer PR/event. I'd be happy if they do a few informative sessions on the updated OS.