All the potential that is there for Portal?
Yeah, to merge it with HL2 Ep3. That was the next evolution of Portal, to bring it into real world levels and mix it with combat scenarios. Between the original Portal, the challenge rooms, the user made puzzle levels, the Portal puzzle formula has been done. A lot of people were hoping that Portal 2 would just be HL2 ep3 which would feature puzzle elements streamlined into the rest of the adventure. That seemed like the best course of action to keep both franchises fresh.
But who knows, maybe Portal 2 will be real world stages with combat. I mean if it's a "full-priced" game, there's a decent chance it won't just be puzzle rooms.