So it seems to me that a lot of people are keen on the idea of whatever new region Sun and Moon takes place in having a link back to Kalos in the same way as Johto did to Kanto.
My main question about that is, is it plausible? As I've said before, every generation so far has brought something new, graphically speaking, to the table. Gen 2 brought colour. Gen 3 brought richer colour and more detail all around. Gen 4 brought 3D modelled overworlds. Gen 5 touched up on that and added the animated battles. Gen 6 brought fully 3D overworlds, interiors, and battles. Going by this pattern, one would expect something new to be brought in Sun and Moon. What that may be, I have absolutely no idea. Maybe it'll be something as small as a stylistic change.
Whatever it may be, it will presumably be reflected in the entire region. Which makes me consider how they would approach making Kalos a playable region. If there is a graphical upgrade, then would it not be a huge, and somewhat unfulfillng(?) task to recreate Kalos in a new style? Given that regions are composed of 3D models nowadays, I imagine worldbuilding is a much more intensive job than it was back in the early days, so putting an entire extra region in a modern Pokemon game would be a big bite to chew. Maybe too big? I don't know. I'm not a developer.
Of course, this is all on the assumption that there will be a graphical upgrade. Maybe not. Maybe they'll just stick with what they know, and not try to make any improvements on their modelling engine or any of that stuff, so they would just copy-paste Kalos in (which I personally would consider...questionable). We'll see.
P.S. regardless of the whole 'graphical upgrade' thing, the actual storage space of the 3DS card might end up being an issue. Wikipedia tells me they go up to 8GB. Is that enough for modelling two entire regions?