I'm rather impressed that this thread has stayed on topic and didn't devolve into some kind of pointless debates. There is so much potential with this idea. They could use the Garlean invasion and the resulting wrath of the elementals to remap the Shroud very easily, kinda like the World of Ruin in FFVI.
However, don't forget there are areas of Eorzea that we haven't seen yet, like Ala Mhigo, Xelphatol, Dravania, and Sharlavan. While these areas would help bring in some new excitement and diversity, we would also need to have a reason to go there outside of a quick class quest. ATM everyone stays in Ul'dah because of the central location and the better leves. They will have to redistribute the mob types, ranks, and party leves to force character/player progression and skill, as well as give us an incentive to leave Ul'duh.