I would hope that very issue is now being considered in the halls of GM as we speak. I believe the issue is plant re-tooling time (converting a Saturn plant to Kappa takes a year I read somewhere). If that can be pushed up I'm sure they will do it.
I think there best bet would be a spring delivery. Bob Lutz did the whole solstice thing out of the box. This is a summer car and GM is in Detroit where there are four seasons. That being said the car would sell much better in the spring than in the fall when new model year cars come out. We will just have to wait and see.
The fall timeline might be conservative, but they have a lot of steps between building L series Saturns, and Kappa based Solstices in that plant. Plus they will want to put in a lot of development and improvement work on actual factory made test mules once it is up and running. I would hope they are aiming for spring/summer delivery, but they obviously are thinking that is a best case scenario where everything works well and there are no delays. Best bet is probably late summer/early fall (labor day or later?).