I'm honestly expecting a very big way to end generation 6 with the next game, and I strongly suggest a prequel. I have a few reasons why.
1. The obvious war that took place 3,000 years ago.
2. There's reference to the war 3,000 years ago in Black and White through an item called the "Relic Copper" or something. It's virtually useless other than it's high value to collectors, but the fact is, they have the data, which means they've been planning this for a while.
3. Even though the cave in particular serves no purpose in X and Y but to house the Bannettite, the Chamber of Emptiness sounds too important to ignore.
4. The mine which houses Zygarde.
5. Ghost girl.
6. The messages in Lumiose Station.
Either prequels or sequels, either way, we need answers. I don't think Gen 7 will be coming for at least another year or two because next year, 2016, will be the 20th anniversary of Pokemon, and we still need to see what they'll be doing for this year, or maybe this game will be the 20th anniversary game.
also, Pokemon Z probably won't be the title. As obvious of one it would be if we were still following gens 1-4 title predictions, it would still be prone to jokes like "OMG ITS POKEMON Z WHERE'S GOKU" and what not. X2 and Y2 also seem unlikely to me, personally, but I could be wrong. However, I do think that we'll have a singular title, if not just to help bind everything together.
Overall, I think that they will try to connect as many generations in the wrap up game as possible. In Pokemon ORAS, it's said that mega evolution was introduced by a man who visited Hoenn some 3,000 years ago (or something along those lines), but there's another fact that heavily concerns me
This Hoenn that was introduced to us is a parallel one to the RSE, and to a certain extent, any past iteration of it in the past games. For one, the plans for a Battle Tower are in place, but this somehow takes place at the same time as X and Y. 2, Zinnia herself says that the meteor would destroy a world with a Hoenn similar to ours.
How does this connect to "Z"? I think that the next game will make use of already canon pieces to create an extremely over the top experience for us. Interdimensional travel may be asking a bit much of the series, but I won't say it's entirely impossible. In fact, I want to say that it's something that will happen in a future game, whether or not they make use of it now or in future generations is in the air. However, they can't just introduce the possibility of an alternate dimension to us without an explanation.
Whether or not Zygarde will be the mascot is debatable. I believe he will serve a VERY important purpose in the next game, but what purpose? I can't say. Fusions, however, I believe are out of the question, because that's a thing already introduced in BW2, plus it wouldn't make sense, given that there's textual proof that Reshiram and Zekrom, plus Kyurem, were originally one Pokemon, while we're given vague information about Xerneas, Yveltal, and Zygarde. All we know is that Xerneas is essentially Pokemon Jesus, Yveltal is a death vacuum, and Zygarde supposedly keeps things in order. I want to say the next game should deal with major life and death scenarios, such as a spirit world, but the likeliness of that is very low.
Either way, I'm willing to suggest that we will be seeing legendaries part of the story that have nothing to do with the current lineup in X and Y. With Hoopa's ability to warp Pokemon to other places, it's highly possible, but I also see Mewtwo playing a pretty important role somehow. Why? He was given not one, but 2 mega forms, and there's one conveniently located in the Unknown "Dungeon" with his mega stone. My evidence also comes from the fact that Pokemon "Purple", along with a variety of other titles, were copyrighted a while back (I believe anyway, I could be wrong here). At any rate, Kalos is going to be very chaotic in the next game.
Also megas for the rest of the starters. It would seem very unfair to introduce megas for Kanto and Hoenn and ignore the others, especially Johto, who deserves a better boost when they're being outshined by the likes of Sceptile, Charizard, and Greninja. My further claims comes from the fact that they practically gave us the Johto starters in their final forms for FREE in our Pokemon Banks with their hidden abilities. I'll also throw in megas for our current starters for sure, since we don't want to outshine them more than they already were by the mega Kanto starters. You could argue that Pokemon such as Greninja don't need it, but I will say Pokemon like Chesnaught could benefit, and also argue that Garchomp, Salamence, and Metagross were already well off without their Megas, yet obtained them, heck even Rayquaza's Mega, who became so much more powerful now and STILL has a slot open.
Before I finish, I would also like to point out the possibility that we still need to revisit Kanto in some form this generation. You could argue that we don't need to because Black and White didn't, but 1. They were already pretty secluded and it worked for them because it was like starting from a blank slate. 2. Again, the 20th anniversary tells me that we will see it in some form, just look at FRLG. To me, this could take the place of "Z", or it could be incorporated in a Johto esque style revisit. The thing is, it's a high possibility, IMO, especially given our Megas. This also poses the possibility for Blastoise and Venusaur to get secondary Megas. As awesome as Charizard is, Game Freak probably got a lot of backlash for giving our flaming dragon special treatment, and it would only be fair, really.
