Certain? Usually overreach of "teh interwebz". The reason many are hopeful is that the circumstances can easily be read to support such a thing (just as they can easily be read to remain business as usual).
Synching up major set releases doesn't mean duplicating the Japanese distribution model 100%. As I have zero idea of what sales are like in Japan, for all we know they'll simplify Japanese distribution a little, while upping overall releases a little more everywhere else. Pure speculation on my part, of course.
Then perhaps you need to ask more questions? I resisted posting a simple "I don't get why someone wouldn't want the sets to be synched up?" response because that explains nothing.
Many of us are tired of the divide; it is that simple. We don't like constantly having to follow up the Japanese game. Yes, sometimes it benefits us; we can get an idea of what does and doesn't work in a set and start from there. Ignoring the future (that is, not paying attention to Japan) can have harsh consequences, but as we know it can't be relied upon either as set composition changes.
Ether being delayed is probably the best, most recent example; a lot of deck testing went to waste, plus several cards that would have at least gotten a small window of play before the next set didn't; Ether/Pokédex had potential but was no Hypnotoxic Laser/Virbank City Gym.
Tell me though... what is the real advantage of remaining separate? It might be different if 1) TPCi was allowed more influence over what cards we received and 2) I trusted them to use that influence. They don't and I don't so it isn't like they can allow good Japanese side decisions through while shielding us from the bad.
