Thats the way I understand it as well, they would either have to restart the production of PWR2's or shoe horn in a pwr3 into the astute hulls. Cant imagine anyone who knows enough about the sub/reactors would start talking about it on public forums. So we will be still be waiting another 12 months of so to see what thier plan is.
The astues in building all have pwr2's. The SSN(X) will be designed around PWR3