Perhaps they will do a prequel that shows how he became Dark Helmet? If they did it like this, then they wouldn't necessarily need Moranis although for me he would be missed.
It doesn't have to be tied to the SW mythos so much this time out -- there's plenty of sacred fantasy franchise cows that need a good kick in the pants.
I suspect George's penchant for re-editing the OT, Jar-Jar, the fact that no one notices Palpatine is Sidious, Amidala's elaborate hair-dos, Yogurt fighting, and the Clones (cue an anatomy joke) probably will provide some laughs.
I don't think I could stomach another Matrix "bullet-time" spoof though, that's just been way overdone.
I suppose they could riff on Lord of the Rings and Harry Potter also (maybe have young Dark Helmet kill Harry Potter to begin his descent to the Dark Side).
Shawn, I don't think Brooks ever intended to make that "sequel", it was just a device to hang some more jokes on at the end. Some pretty good ones, too, with "Hitler on Ice" and "Jews in Space."
I think it would be a great gag if they watch "Spaceballs: The Movie" again and you can't even see anything because the whole screen is filled with CGI creatures which obscure virtaully everything else.