I don't have much love for X (at all), but to be fair, I think that even if it was linear as hell (main reason I dislike it) it wasn't as obvious as XIII, where it was painful except for the time you spend in Gran Paals; it didn't feel like an actual world.
In X, I think it was more justified by having Spira being a bunch of islands under a giant whale's threat, so it served its purpose more than in XIII, even if there there are also reasons (they're persecuted and Gran Pulse is a wild world). Spira felt like an actual world that was that way because of its story (whether I liked it or not), while XIII's Cocoon and Gran Pulse didn't feel like that, wasn't 'credible' (for me).
Regarding XV, I think it's basically going to be like XII but with bigger areas maybe and much more seamless.
Basically, taking IX's map as an example, the entirety of 8 (Cleyra <3) would be seamless, while if you want to go to, say, 33, you'd have to go through some sort of transition, because both places are separated by chains of mountains you can't climb. Of course, much more realistically scaled than in the PSX games: