According to those rumors, a villain will take Jack-Jack under his wing in order to turn him into a copy of himself, after Jack-Jack discovers that he has special powers but has trouble controlling them properly.
The boy will likely go through a lot of trouble because of this, and he could have a very interesting story arc that spans across peculiar developments that we wouldn’t have expected to see for him in the first place. His original character wasn’t exactly assuming and not many fans really expected to see this kind of development for him.
But that’s all still up in the air. Brad Bird is relatively secretive about how the film is going and what kinds of ideas he has for its plot, and it would be interesting to see where the director decides to take things next.
He probably has one or two tricks up his sleeve though, as he most definitely understands the importance of this installment in the franchise and knows how much fans are looking up to this film, so he will want to put in all the effort he can to make sure that it works out as best as possible. Because of this, it’s pretty much guaranteed that there will be some surprises in “The Incredibles 2” that aren’t even being discussed in the rumors right now.