I'd probably expect that if we have a "zoomed in" mode with any vehicles/chocobos, I'd expect that there'll be particular areas of the world map that are explorable in "zoomed in" mode, and others that aren't. There's a lot of dead space, but I'd expect certain Forests or areas around towns and whatnot to be "zoom-in-able" which could even just be a simple button enable/disable like where you can/can't land the Highwind in the original game. If they do that, it'd also reward wandering around on the world map to find all of the explorable areas a lot like the OG did as well. Some might also be tied-in to events you need to complete first (like finding Zack's gravesite).
Likewise, while in a vehicle / in those areas, you'd be able to have an "exit to world map" only when you're outside of whatever area qualifies as "World Map" but that also doesn't quite answer how/if you'd be able to "zoom out" without a vehicle. If it was me, I'd have Cloud & Co. actually start out traveling out from Midgar on the Bike & Truck (thus why you have the minigame to keep them both from being wrecked). Logistically that would let them get around decent distances, but they'd still also be hard-stopped & forced to proceed on foot once they reached the Chocobo Ranch, since the bike & truck couldn't cross the swamp.
Then from that point on, you'd have access to a generic Chocobo to call as a form of World Map transportation, or choose to exit into a vehicle you have in the area instead. Eventually you could start breeding Chocobos and having one in a stable set to be able to call those specific ones whenever you're exiting to the World Map. That gets over the scaled-up-cloud-on-a-world-map by replacing it outright for you riding Chocobos which makes sense to see from a zoomed-out perspective, since eventually they're gonna be special terrain vehicles.