GM has been very quiet about the top. Recently I saw something that indicated that the tops on those prototypes were modified Corvette tops that were rigged up to allow the drivers some protection from the elements while testing the prototypes. I have no idea if this is at all true or not either. I forgot where I read the info.
I am hoping GN shows a prototype with a production spec top at the Jan 2005 Detroit Auto show. I would imagine they will offer an updated prototype to keep the Solstice "hot" and prepare it for introduction later in the year. But for now, we know very little.