I too hope they pull a Johto. Having the whole gang, Brock and Dawn included travel to Johto. Mainly because the Johto games were on the same console as the previous, much like these ones. So I would like Ash to go to Isshu with his Sinnoh team, and then have Infernape become a Charizard, and stay in some place, where it can be called upon. And the rest of the team are then dumped off at Oak's one by one, with the exception of Gible who will then grow stronger and eventually evolve into Garchomp, then leave his team to make room for another pokemon. Although, none of his Sinnoh team would fight in a gym battle. But they would all come back for the league.
Also, no, Paul released Chimchar, Ash has trained it so it is what it is now, why would it go back to the trainer who treated it badly?