I think Cynthia, Lance and obviously Gary are not real Champions because they already lost their Champion titles to their games' protagonists, knowing that gens 1, 2 and 4 have already happened before B2/W2. That's why their all battle titles say "Trainer" not "Champion". I think they are just decided to be labeled as Champions instead of protagonists because they have more defined teams and aren't completely silent. Steven might the only real Champion left, seeing how in HG/SS he still says to be official Champion, meaning that most likely R/S/E take place after B2/W2.
Its more fan speculation with little to no support that Hoenn comes after them in the time line. Why would they make a game that is so far in the time line so early? Why were the new Special Pokeballs that were invented in Gen 3 still in Gen 4 if Devon Corp hadn't invented them yet? Why was scott Searching around the world to test his One of a Kind Facility if there were other versions in Kanto and Johto? Yes Scott Opened the Battle Fronteir in Emerald, it wasn't opened/finished until Emerald's Post game. There are many facts from the games that support its placement with Kanto or between the three year period between Kanto and Johto.
Steven is still the Hoenn Champion meaning Wallace is a Gym Leader, so they are following Ruby/Sapphire story if Steven being in the World Tournament is any reference to Hoenn games. We've been told to stop discussing this in other threads, so lets stop please neither side is going to accept the other, all major sources have Kanto and Hoenn at the same time, so unless Gamefreak comes out and says that Hoenn is in the future it isn't.
I replied to this in new thread in Gaming Central.