Actually it is possible to assume that the creation of the regions(or at least the findings of eachv region) follows as so:
Sinnoh > Hoenn/Unova > Kalos > Kanto/Johto
Okay so let me explain. Using information found on Bulbapedia, it states that Arceus created Sinnoh, as well as Pokemon themselve, or Mew, who was the ancestor of all Pokemon. During this time, the Golems(Regirock, Registeel, Regirock and Regigigas) as well as the Hoenn trio AND the Lake guardian, created the Pokemon world and Humans alike, as human traits are most likely stemming from the Lake Guardians(Azelf, Uxie, Mespirit), as they represent something realted to human nature which is Knowledge, Emotion, and Willpower.
So Sinnoh came first. Arceus's desendants, Palkia, Dialga and Giratina, watched over the world as it was. It is shown as the Golems, Lake Guardians, and Creation trio are found in Sinnoh. But that is when the grudge between Kyorge and Groudon began. Their fighting created Hoenn and Unova, by using their Primal Forms. So we all know that Kyorge and Groudon migrated to Hoenn and fell into rest, leaving their Primal States behind them. But everything isn't as Black and White as it may seem(see what I did there :))
Unova was created, but it was far more suitable for the legendaries to live in, as at this point, Humans were overpopulating in Sinnoh alone, which as History tells, pretty bad for people. People need space. So did the Golems and Lake Guardians.
The Golems and Lake Guardians ended up migrating. The Lake Guardians going to Unova and the Golems going to Hoenn. There they slept for some thousand years until something happened and BAM Kalos was created(I still have yet to piece this together). In Kalos, there was a boom in Pokemon species and had plentiful resources.
Of course, humans are greedy so they move here from Sinnoh. A more centralized organiztion was established, with the Parfum Palace symbolizing some sort of Monarchy. Here the followers of AZ's brother, the king and the people in some sort of Pokemon War for Independence. We all know the tale, AZ uses his weapons and in a literal since, ****s up everything. Pokemon species died, which explains the low quantity of Kalos Pokemon in XY, hint hint and the Monarchy is abolished.
Soon after ancient Pokemon migrate to Kanto and Johto, like the birds, the Tower duo, the dogs and the Mew duo. Afterwards humans population migrated and spread, civilizations wete built and the Golems and Lake Guardians continue to migrate between Hoenn and Unova, and ultimately stopped at Sinnoh before the events of the games begun. Then the events of the games follows the timeline:
Kanto/Hoenn > Johto > Sinnoh > Unova > Kalos
But that in hindsight is just a theory. But that's my spin on it.