Yeah I too wish they'd connect the 2.0 and 3.0 cities into one map. Kugane is super detailed and super big. So is the Crystarium, and 6.0 is coming with at least two more large highly detailed cities. The only limitation to recombine the 2 maps of the city-states is disposition of the staff to do it.

For some time I wish they'd convert some of the surrounding areas from ARR into one map as well (so for instance combining Central and Western Thanalan into one map). The "long tunnels/valleys" connecting them wouldn't bother me. Most people would fly or teleport anyway.
However, I don't trust the map designers to do it without ruining what makes ARR maps interesting. To me ARR areas still have the best overworld design, with detail and lore in almost every corner, unlike the maps from 3.0 onwards where you have an excessive amount of flat barren space with nothing of interest.