I want to see Dia use the Trick Room attack *-*
And I think he'll have a Gastrodon...
Maybe a Ambipom, a Floatzel, a Rampardos or a Surkit(lol) to Pearl.
And Wormadam/Vespiquen, Smoochum, Happiny or Cherrim for Platina.
And 1 stupid question, what is IMO? '>.>
Yeah, I suspect Trick Room will be used in a critical situation in which Diamond reverses the battle tide...
Ambipom will most likely appear with Gold when he shows his face in the future...
If Pearl is going to have a speedy Pokemon, Yanmega is the most decent one or even Gallade (if it is not with Platina), or maybe a Mime Jr. Otherwise, he might just have some "showcased" Pokemon like Lumineon, Pachiritsu, etc. (just like how Ruby ends up with Popo, which in my opinion does not show any smartness at all)
Platina has a better range of Pokemon to choose: Gallade, Leafeon, Glaceon, Togekiss, etc.
Diamond is still the champion, most strong Pokemon are bulky: Mamoswine, Magmortar, Lickilicky (which I think is confirmed), Electivire, yeah, you name it...