I don't see why some people think its highly unlikely.
Looker even said himself that N was spotted in a far away region, and that he was going to go look for him. I don't see the point in foreshadowing that for no reason. If Cynthia's statement about the world championships came true in B2W2, I don't see why Looker's statement wouldn't come true considering that part was pretty much the complete end of the story and was the message we were left with.
And to the people who said they didn't have time, B/W finished development probably around mid-2010 if the game was released in September 2010. That means they have had almost 2 years of development for this game WITHOUT B/W (I'm almost certain to believe that they were working on B2W2 alongside B/W so they knew what to put in, leave out etc). They have had more than enough time.
If we do get another region/set of islands, I don't think it'll be an older region. I would think that it would be a brand new set of land we have never seen before (possibly like the Sevii Islands, except it'll be one big land mass rather than separate islands).
It's still not certain, of course, but I think it shouldn't be dismissed either.