Are we going to be able to catch both Dialga AND Palkia in Platinum? If would make sense, seeing as we could catch Kyogre AND Groudon in Emerald. I think the methods of catching them will have to do with the Torn World, because that probably has something to do with you(the character) not catching Palkia and Dialga before the catastrophe at Mt. Coronet. Maybe they tore open this new world? I think something along those lines should be expected.
I don't know if this has been answered yet, but I don't feel like reading through 64 pages, so sorry.
EDIT: You got to it first!
Posts like "I don't want to read through[xx] amount of pages." Are stupid.
There is a search thread button on the top right corner you know.
Any way no it hasn't been confirmed that both Dialga/Palkia appear in-game but it is assumed because of past gens.