The beauty of G3 is that each lineup has successfully attracted somewhat diverse crowds. Players like Eric Johnson, Petrucci, and Yngwie(who I despise) all brought in their own followings. Though I love Satch, I find his music to be much more predictable and significantly less awe-inspiring than any of the other previous players. He is simply no longer a "draw" for me. I mean, who the hell hasnt seen him live? He tours often, and plays 3hr shows. I will always attend G3, but never specifically for him.
That being said, Tony Macalpine would be amazing, as would Romeo. Whoever suggested Steve Morse is a genius had a great idea. A return of Eric Johnson would be killer too. And didn't Kenny Wayne Shepherd fill in on some dates when EJ dropped off the tour? I don't think I'd welcome him back.