Just popping up to add that I'm still following the thread too, still a fan of Pearlshipping, I just don't really post much as I don't really have much to add to speculation, sorry. I'd love to see Dawn show up again in the main series (though it'd sure be odd to see her drawn in the new art style), but its always hard to guess when. It'll probably just be at a random point, like with Misty just suddenly showing up. At least May's cameo tied in surprisingly well into Dawn's own development, but then they both share the same career so that helps.
I'm still mostly expecting Dawn to show up, although I am thrown off by how big the reset of the show was. I hadn't watched the entire episodes until they were dubbed, and ugh, they had to re-explain to Ash the whole thing about the Joy family. Hopefully he won't get amnesia about too much other stuff, like old friends, if/when they ever show up. At least Dawn actually had her own special dedicated to her own journey.
Sometimes Gyms go fast, sometimes they go slow. I mean during Sinnoh there was what, a year-long gap between Ash's seventh and eighth Gym battles? Although there was a lot happening in that year (Dawn's Grand Festival, the Team Galactic finale, etc.). I remember the good old days when Ash went through the whole of Kanto in just a year, wow that seems insanely fast these days.
Its always annoying when the stretch between Gyms are stretched out, although during Hoenn and Sinnoh that was partially because the series was also focusing on Contests, but they do have to wait for the next generation. Although B/W's pace is almost unusually fast. Less than a year since B/W came out, and Ash is already past his third Gym. At this rate B/W could last only two years, though I expect there'll be bigger gaps by the later Gyms. During the third and fourth gen, May and Dawn shared Ash's lead character role, so there was more stuff to do, but not sure what B/W will do yet.
Unless they really do go through Unova that fast, then go to Hoenn or something when the Ruby/Sapphire remake hits. That would tie in nicely to where Dawn would be, kind of like how Misty showed up at the beginning of the Battle Frontier saga (just wish I had actually seen those episodes, unfortunately). Well, one can hope anyway.