Really. I imagine they will announce it this weekend, but all the evidence points to that. Unless they only plan on having him do a Green Arrow/Green Lantern book.
But let's remember a few things:
1. Geoff brought Robinson back in.
2. Geoff wanted to have a writer he loved working with partnered with him on the Superman titles.
3. Geoff, I believe, expressed wanting to make the JLA/JSA crossover stories a semi-regular thing.
Mind you, the two working out some sort of Green Arrow/Green Lantern Hard Traveling Heroes thing could work, but it would seem to be more than the properties can support. Has to be Robinson on JLA after McDuffie's run ends.
I'm sure it will be great, but McDuffie has certainly gotten screwed over (albeit with a regular check) in the last year, becoming just a place holder for JLA and Fantastic Four.
Edit: D'Oh...while it wouldn't render my guess completely incorrect, THE SILVER AGE has been floated as something he might do. That would make a helluva lot of sense.