Some people don't quite seem to get that it's not as simple as 'just remove the transition barriers and load screens and let me walk that distance between maps', as some have said, the 2.0 maps really weren't designed for seamless zoning. They aren't the 1.0 maps imported into 2.0. All of the 1.0 areas, Thanalan, Coerthas, La Noscea and Black Shroud were completely rebuilt from the ground up, this is also why getting the 'missing maps' from Coerthas and Black Shroud is not that straightforward.. because they'd have to make them. The way these 2.0 maps work is by design and they're not designed to interconnect, which means that it would require considerable work to 'glue' these maps together into one whole in a way that doesn't feel half assed.

The towns.. the city states, I suppose one could argue there.. as all three are in essence mostly the same maps from 1.0, I dare say you could probably return Ul'dah and Limsa to single map city states with a degree of effort that would be within reason. Gridania I'm not sure about.. Gridania had these really lengthy tunnels in between what is now Old and New Gridania.. I suppose it depends on if they're entirely intact and just inaccessible.. or simply not there at all.

Personally doing away with the duo zone cities from 2.0 and 3.0 is really something I want.. as there really is no reason for it to be that way anymore.. as Stormblood and Shadowbringers have shown us. But that means putting dev time into turning for example Ishgard into one functional city that flows seamlessly from Foundation into The Pillars.. rather than putting it into new content.. and that's always tricky.. it's always easier to justify making a new shiny than it is to polish up the not-so-shiny old stuff.