Seeing as it's been 17 years since GF made a sequel generation, it's hard not to be pessimistic. Nothing about what I've heard about SM so far indicates any kind of connection to Kalos or Zygarde. Just the fact that SM will be set in Hawaii (aka. nowhere near France) should be enough of a giveaway.
To be honest, I think the idea of sequels is dead as long as Masuda is still in charge of the games. Even though he actually hasn't come out and said it, he doesn't seem to be a fan of sequels. The very first games he directed (RSE) went out of their way to break ties with the previous games, and every single consecutive generation since then has been an isolated entity with no connections to any of the previous gens.
From what I've read, even B2W2 were only made because of executive meddling from Nintendo, who thought that sequels would sell better than the standard third version on the then dying DS. If it had been all up to Masuda, we probably would've just gotten a generic Grey version, instead.