I think prohibited areas would include military no fly zones, the Mexican boarder, and all TFRs (ie stadiums, Disney parks, VIP movements, military training exercises, etc.) They could probably also lock out prisons/detention facilities in the future but probably since they are relying on Airmap.
I guess we are both making assumptions. Mine is that airports will not be geofenced. Your's that they still will be. I guess I'll just wait until December when the program is launched to know for sure.
Edit: I just came across this article which has better explanation than the one linked above.
DJI is removing mandatory no-fly zones from its drones
Sounds like airports will be unlockable. He mentions DC, prisons, and nuclear power plants as examples of permanent NFZs.