They already have the Gen I-VI models made for the game, so they really only need to develop the new generation and the world design. They did a lot of the "qHD" or "HD" work for Gen VI.
Yeah, although the overworld graphics could do with an overhaul. I'm more referring to the leftover bits of Gen VI content to deal with, like Zygarde's formes, AZ's Floette and the like. It may just be that they don't intend to give this stuff its own game, but it would be a distinct change of plans if that's the case.
True. But without Z, I expect a very early NX Pokemon game rather than B2W2 scenario of a "3DS has launched, here's a DS game".
I'm agreed on that score. If Z has indeed been scrapped, it's to make room for a new generation significantly earlier than we otherwise might have expected it, IMO- maybe even just a handful of months after the NX launch. Hell, maybe Game Freak were informed of Nintendo's plans to introduce the new console generation earlier than they had initially anticipated, and changed their plans to accommodate it?
Interestingly, there's also a fair bit of mystery surrounding this year's Pokémon movie, and what Pokémon it's going to include. We know that it's going to focus on Volcanion, as that's been revealed uncharacteristically early- alongside the movie's first reveal, in fact. Generally speaking, the promotional campaign for each movie over the past 7 or 8 years has two big Pokémon reveals leading up to its release- this could be the announcement of a hitherto unconfirmed but still known Mythical Pokémon, or the reveal of a new forme for it, or just flat-out a new Pokémon. The first of these reveals tends to happen in February, and the second in April or May, in order to space out the reveals and to drum up interest. The primary legendary, however, may be revealed in advance of this if they have more reveals to get through- back in 2012, for example, Genesect was revealed months before the film was announced, giving them space to announce Sylveon in February 2013, and Mega Mewtwo Y in May 2013. Volcanion's early announcement heavily suggests that there's another few Pokémon reveals to come, but what? Even if we assume that one of them is another Volcanion forme, that still leaves another one to go. It could conceivably be a Mega of a previously-existing Pokémon, but I'd suggest that it's not overly likely. Movie reveals are often tied in to distributions of Pokémon, be it to unlock them for the first time, or to unlock extra content or formes from them. One of these distributions will undoubtedly be Volcanion, but what will the other be? They went out of their way to ensure that all non-Mythical Pokémon were available to be captured in X,Y and ORAS, Zygarde's arc and promotion is being dealt with in the anime, and they are now distributing all of the Mythical Pokémon over the course of the year- if they were indeed giving a major legendary a new Mega with a starring role in the movie, you'd have thought that they would have held back a bit. None of this is conclusive, but it does lead me to think that we might be on the cusp of them drawing the curtain back on a new Pokémon generation within the next few months, which in recent times suggests that it's going to be shown off sooner rather than later.
tl;dr There is substantial reason to believe that we may start seeing the new generation of Pokémon this year, and this may indicate that it's starting sooner than we expected.