Why Kalos tho? Kalos was boring and awful.
It would, however, be really neat if we could return to other regions in general in Sun/Moon. Like, just take a boat to other regions and give us MULTIPLE MAPS worth of post-game, high level gym battles and all. It seems a little TOO ambitious, but it's definitely a nice thought.
Oh gosh ditto on what you said about Kalos. I wouldn't want Kalos to be the post-game region, for sure. The post-game in Kalos was a total disappointment.
Unfortunately, I know Nintendo won't do something as ambitious as having multiple regions in one game, as I think they've stated before it just wasn't possible through the laws of Pokemon games (ridiculous experience yield among many other things) and that it just isn't possible to have on a DS cartridge....This was mentioned before the release of the 3DS though, and I think that if they pulled off HGSS on the regular DS, then maybe it's technologically plausible...?
Sadly I don't have a source. I only heard from a friend and took their points without a grain of salt, which I maybe should have, but the explanation seemed good enough to me. Every day I cross my fingers for a region I really like to be recalled and perhaps brought in for post-game... but any region being post-game for gen 7 just doesn't make any sense to me. I'd say Unova, because if Unova is based off the USA and Alola is based of Hawaii, maybe Unova would make more sense? Ah, but that's probably my own bias talking. Not to mention the Gen 5 games even had their own sequels. I don't think Unova is making a return anytime soon. ):
Still, I will stay hopeful!!! Maybe Gamefreak will listen to our critiques and apply them. 6th gen was a total 180 from 5th gen because of the many critiques they had. I'll be optimistic about Alola! I've liked a lot of things I've seen so far.