I definitely think there will be a GM, it doesn't make any sense not to have one. That's not how a development cycle works. On another note. I'm on DP4 with a rMBP and it does have a few small glitches and issues so I think the GM is still in the works. I imagine they are fixing these rMBP issues just because they are touting the rMBP as "The Greatest Macbook Pro We Have Ever Made!" They need it to perform perfectly.
On a side note, this thing has wings and it knows how to use them. Would be nice to get a few of the UI glitches fixed so it's a bit more smooth but even with glitches it's lightning fast.
So my guess Monday or Friday but definitely a GM is coming. A development lifecycle of this magnitude always has a GM.
Just my .02 of course.