Portal 3?
Gels were presented in a "Tag: power of paint" game for the first time as far as I know, and they collaborated with Valve to make these testing elements into Portal 2.
Yes, but nobody expected them to add gels after playing P1.
I think nobody expected them to add any other new testing elements, like funnels, lasers, faith plates, etc. after playing P1. Pretty much everything was new in Portal 2.
True. Very true.
Although the Blue Portals people did manage to make lasers, but they acted more like real-life lasers would.
If I remember correctly from a conversation I had with one of the Valve devs...lasers, tractor beams, and light bridges were items that the original Portal 1 team had experimented with but they didn't have enough time get them to a releasable state. Since Portal 1 was more of a demo, they were keeping it fairly simple as well.
Wasn't that from the final hours of portal 2? 
I also remember this.
Not sure where they'd take the story next, unless they start with a new protagonist but I'd play it.
Wasn't that from the final hours of portal 2?
I also remember this.
That is possible... or we were in a group conversation 
Gravity altering, more outdoorsiness, different cubes, colour coded lasers, altering the portal gun etc.
Gravity altering is hard unless you use the PUNT cube. More cubes and outdoorsiness, maybe.