I'm thinking that the collection of such anticipated films together aren't really going to affect The Incredibles 2. After all, seeing Avengers Infinity Wars 2 or Justice League 2 isn't going to stop anyone from watching Incredibles 2 (boy those are a lot of 2s
). There's also how Justice League might not do so good, and even if it does, The Incredibles 2 is still really highly anticipated, so it'll make lots of money in the box office anyway.
Also, on a separate note, I don't think the movie is going to be about Dash, Violet, or Jack Jack rebelling against their family or that it'll include Bomb Voyage or the Underminer.
Another thing too is that I agree and it's way too early for Bird to release plot details. If the film is coming out in three years, I would rather wait for a synopsis than get it now, for the sake of avoiding a The Incredibles 2 knock-off by other studios and because plot details three years in advance is just kind of illogical.
Well someone (other than me and maybe Canadian Pixar Fan) gets it right, although I still think it'll focus on the kids in the end as it's the only logical direction they can go at this point in time and it's highly expected as they can't really go in another retirement-like plot like the 1st film pulled off as that would be revisiting old themes (I think it might focus more on Bob and Violet's parental relationship a bit more as father/daughter since we never really saw them interact all that much in the 1st film aside from a few scenes), also Cars 3 has the retirement story down already.
I still think Bomb-Voyage and Underminer will appear as cameos to tie into the events of the 1st film (plus fans have been waiting for that bombing criminal to get his dues for over 10 years and not having him there would be like a punch to the face to those fans), plus Bird mention he wants to use the 1st film's unused stuff for the 2nd film to link back to the 1st film's events in some form (similar to how other Pixar sequels have done over the years).
If we get any plot details at all, it'll come at D23 next year or if not that, then maybe in mid-2018 (right around when Toy Story 4 comes out) or even at the Disney Shareholders meetings (which is how the 2nd Incredibles got confirmed).
The one thing we can kind of possibly predict 100% would be part of the voice cast regarding the family and Frozone (Craig T. Nelson, Holly Hunter, Sarah Vowell and Samuel L. Jackson are all pretty much coming back (Jackson more or less confirmed his return just as the sequel was announced, Hunter also partially teased she was on board no thanks to that Collider interview about BvS), Dash and Jack-Jack might get recast due to Spencer Fox being too old to voice him (pulling a Nemo on Dash) and J-J's up in the air right now as we don't known whether or not he'll still be an infant or a young kid at the age of 4-5 when the sequel's news gets dropped).