I'll be happy with a localised region of the world, ala Ivalice. FFXII managed to spread the action and plot across multiple continents, albeit at a certain converging point of three continents, a kingdom, a nuked kingdom, and two empires, so there was still a sense of scale to it, and being at the central hotspot, rather than the fantasy parallel of something small and localised like say, a regular early-C20th Balkan conflict (one of which did eventually lead to WW1 I am aware, but I digress...).
If you seek to build a fantasy based on reality, I don't think the conventional world map works. I'm not thrilled with the idea of an entire globe with only a few features and locations identifiable here and there, with most of it being standard topography, because it would look surreal for something FFXV supposedly is trying to build itself to be. It's why I'm picturing something like Skyrim, with immense freedom of movement, but sensible confinement by the physical landscape, or something of an MMO model of say, Guild Wars 2 and what FFXIV probably has: sizeable zones that encourage exploration, and the ability to drive around in a vehicle, passing by the occasional gas station in the desert, etc.
I did glance at the Wiki a while ago, and I did see the UK's Manchester being mentioned as a potential place of influence, so I'm looking forward to some kind of grey, dystopian, northern, crime-ridden city (I kid, Mancunians! Manchester is lovely...most of the time!) with confusing roads. We definitely know Tokyo, Venice and possibly a desert akin to something you find in the midwest to southwest United States will find their counterparts in the game. I personally would love to see a Middle Eastern or North African inspired setting for one of the kingdoms, and I know FFXII incorporated a bit of that with Turkish architecture amidst South Asian ones. An ancient Chinese setting would be something I'd also love to see, akin to Jade Empire, and Age of Wushu, although I'm rather aware of the current tensions between Japan and China that can sadly encroach beyond the political realm being one major blockade for this.
I'm also a little wary. When your buzzwords are "a fantasy based on reality", I fear the non-presence of some truly fantastical, alien fantasy landscapes. They're things that fellow JRPGs like Xenoblade, and various MMOs excel at, and I wonder to what extent the designers for FFXV were allowed to let imaginations run wild. True, not every RPG needs to let imaginations run wild, and I agree that often it can lead to gaudy, over-designed, wtf-is-this-mess results, but back several years ago when we first saw images and video of Noctis traversing a deserted, post-apocalyptic barren wasteland, I wasn't very impressed by how bereft of anything it was, and I hope for the actual game's sake, its desert region doesn't exactly look like that, which fortunately I'm certain it won't be, because even Fallout's desert landscapes exude much more life.
tl;dr, I predict a part of the world will be explorable. If you're going to have an epic of games, it would make sense to reveal more of the world along with a new direction in plot and characters in a sequel. Heck, there's a bit of me thinking that we may not even be able to visit all kingdoms. If a pivotal player like Rozarria in FFXII could return out of reach, who is to say that any one of FFXV's kingdoms won't be either, especially if one of them is conquered and is thus, rather inconsequential from thereon forth.
