Portal 3 will probably further extend into the backstory of Chell and GLaDOS, Wheatley will probably make a comeback...somehow... but probably play a less significant role. I imagine a new antagonist appearing as well, it would be cool if it was another human.
Everyone should know that I firmly believe that Portal 2 takes place 72 years after Portal 1, so I can't really see a 80-100 year old man doing tests. I think it would be neat if Wheatley somehow managed to get himself on the surface of the moon, and found an abandoned Aperture Science Moon Base or something, and took control of it. You could be a missing astronaut from the Senate Hearing, awaking from stasis when he manages to plug himself into that stick on the wall that let's him take full control of the base.
I believe sequels have the ability to disgrace their predecessors, which is why, in my opinion, Valve would have to put a lot of thought and effort into a quality game. Too many times have I seen companies over-capitalize on popular titles and ultimately ruin them, which is such a shame, and would be especially for games like Portal.
I agree with what many people said here. Let it be.
This game you're talking about suggests it is set at the same time as Portal 2, but from Doug Rattmann's perspective. The problem is: According to Portal's backstory, Doug saved Chell by placing her in stasis in a mobile Aperture Science waiting room. Sadly, straight after, Doug was shot in the leg by a turret, bled out and fainted, I believe he may have been killed. Since Doug was kill 100 years before the events of Portal 2, he couldn't do anything then. If he wasn't killed, he'd have to be 100+ years old. The only reason Chell didn't die of old age was because she was in stasis for the 100+ years between Portal 1 and 2. This was thanks to Doug Rattmann, who died to save Chell so she could escape. I believe this is canon as I am pretty sure it was in the Portal 2 "Lab Rat" comic which I presume was published by Valve. If they were to make a Portal 3, it should be about the time between Portal 1 and 2, also from Doug's perspective. That or it could be set before the two games altogether and work like Doug is the first test subject ever and is
Acutally Cave Johnson's Nephew!
Tell me if you want me to go into deeper detail, but I believe I have proven my point.
Certainly not. I'd place it around 30 years. The level of invasion of the plants inside the facility indicate that some decades have passed, but the relative mantained state of the place (especially seeing how quickly GLaDOS fixed it) says that it couldn't have been so much. If it was 100+ years most of what we see in the first batch of levels would be completely destroyed.
Or they could actually create F-Stop, the prequel to Portal that was originally going to be created. You know, F-Stop? The game that takes place in Cave Johnson time, before they had portals? It was replaced with Portal 2 when play-testers realized that there were no portals.
And the sad thing is, they never even told us what the F-Stop is.