Why plastic (thinking wireless charging is back?) And what SOC bump are you expecting? 823? Not seeing much exciting in there....830 would be crazy, but don't think that will be announced until early next year.
I'm just taking a stab at predictions. I have no idea really.
My logic is they'll try and cut costs thus offering a lower price for the Nexus and they'll want to keep the Nexus from competing too much with the 10 so offering less premium materials is the way to do that. Also bringing wireless charging back to the fray.
The SOC will be a minor bump, so 823, and the two models will be a small one and a bigger one with little differentiation. The bigger will probably have a bigger battery, and perhaps a better camera. And maybe the bigger one will be "force touch" capable since it won't be ready at launch.
These are my predictions. I'm probably wrong, but hey, it's part of the fun.