I'm hoping that since the Kanto starters got a chance to shine in the last BF, the Johto starters will get their chance in this series.
Cyndaquill could evolve and that would be great, but Totodile needs to be showcased and use at least more than two attacks, Bite and Water Gun are stale at this point. Aqua Tail or Avalanche maybe would be cool to see. Bayleef also should be shown since it was one of Ash's big bruisers in Johto.
I don't want to see Torterra, but Infernape would be great since I think Monferno may happen before the end of the DPPt saga.
Cyndaquill evolving = Phanpy evolving
Monferno evolving= Sceptile evolving.
As for the Brains, I kind of like the idea of the line-up changes like last time. While I think some signature pokemon shouldn't be changed, like Darach should have Empoleon, a change of scenery is always good.
Palmer/Battle Tower- Give him Dragonite, but having him as a dragon trainer could be cool. Or showcase him having Heatran and other tough guys from Stark Mountain Area. If I see Milotic again though I will scream. Everyone whose a superior trainer has one: Wallace, Juan, Robert, Lucy. Enough already.
Argenta/Battle Hall-She seems like a fashionable lady, but I couldn't even guess what she would have.
Thorton/Battle Factory: I hope Ash uses Random Pokemon against him. He could use smart/techno type pokemon. Magnezone would be a good use, Gardevoir and maybe some others like that.
Darach/Battle Castle: Empoleon needs to be his main since he is the only one to keep the same pokemon for both rounds. Regal pokemon would be the rest probably. Maybe Pidgeot instead of Staraptor and keep maybe Gallade as like a swordsman.
Dahlia/Battle Arcade: I would love her to have Ludicolo as a dancer. If she followed that trend maybe Clefable and seeing her with that Blaziken might also be great. Please no more Medicham though. Like Milotic, I think we've see enough.