While correct, Sinnoh is not just any old region. DP, and to an extent Platinum, were made in the mindset of them being the ultimate titles, a culmination of the previous three gens before moving on to something entirely new. Its a weird case, as its not the last game before a reboot, and definitely not the last game in the series, but its definitely the closing chapter of one book before a new one started. Black/White was indeed a turning point, and outside of Hoenn Remakes, its all been situated outside of PokeJapan. Its the same thing, and more so than back then, once Sinnoh remakes happen, beyond(unlikely) sequels or god forbid Re-Remakes, the era of PokeJapan is full dealt with. From the next generation on, its all going to be Unova and beyond. I am not saying this out of nostalgia or anything, just that its clear that there is a line between Gen 4 and Gen 5, so once a remake does happen, its not going to be treated as lightly as previous ones.