After N arc assuming there is enough time left for it, i would like to see writers expanding on whole world tournament thing not stopping just on Junior Cup. Junior Cup hardly felt like something you could call world tournament having very small organization for event which is supposed to be on global basis. There were basically no trainers from other regions and whole name of it implies how there might be more tournaments in future.
It would be great having them create several smaller tournaments host by Cynthia in which Ash could participate and fill up time with something before new games come out. Like Senior Cup, Champion Cup etc. offering enough material to support filler arc through some concrete plot going on.
As for older characters, i would like now that Dawn return finished writers continuing in that direction bringing some other popular faces back in third year of BW;like Brock and Misty .
They could in case of full PWT adaptation be among first choices as iconic and important enough to warrant return for advertizing purposes (they are after all part of it) and to serve as link to past providing continuity. And to potentially advance their own storyline, especially in Misty case. Logically traveling to Unova or through Kanto to compete in PWT would make sense helping her to climb up as trainer by improving skills and learning new things from best advancing dream of becoming water master , with BW2 providing outlet through which she can become important to story again.
This is what I really want. Especially since I want to see Misty again.
I believe most people in here would like that, but sadly desire often doesn't meet reality. Either way it would be great to have Misty back knowing how to spice up atmosphere and get some update on her story. She could certainly use more development having several unresolved things going for her.