Someone said that it was confirmed in one of the leagues that all pokemon can be transferred to the league's "zone", without restrictions to 6 per trainer, however, most don't use this, as if any pokemon fight, (other than sparring), the trainer is disqualified from said League.
I personally hope Butterfree and Pidgeot return. They probably never will, but I really want them to, XD Even if just for an episode.
This will be the first time Dawn meets any of Ash's pre Sinnoh Pokemon, aside from Aipom and Pikachu, unless I'm missing something. It'll also be the first time in a few years that we see them.
I personally hope they're transferred to where the league is taking place, just so we can see Paul's face when Snorlax, Sceptile, Glalie, and the likes appear. :P