World City
I think the idea has merit, but I do think that several character options seem to hinge on nature and it would take a lot of doing to develop something to replace the diversity of monsters available through a wilderness. Concerns like these have probably always been an obstacle
That and the massive amount of magic involved as well as the massive tome necessary to give the place any detailed justice.
Even if you sized the concept down to an urban environment the size of FR, the real challenge to overcome is making up for the diversity of environments created by wilderness and urban settings in the same campaign.
Not impossible, but a challenge.
Have you ever considered the possibility of a magically sculpted world like Farmer's RiverWorld?
That place was effectively a worldwide city so effecient that people didn't always need large structures or obvious infrastructure.
I have always advocated the idea that human cultures would really reach their pinnacle when you could adjust the local ecology and environments to perfectly fit your needs. That way we could all live like Jabba. Neighborhoods with this ethic could be run by Druids and policed by Rangers.
Doing this with magic, rather than tech, is a lot more interesting to me actually.
