We think about this completely differently.The zones, I predict, would become isolated and disconnected. Each DM would cart the PCs off to a new zone for every adventure, or to that DM's own zone, and the world isn't "living" in the sense that other PCs/DMs influence the world around you.
I do agree that you need something "solid" to hang a setting on, and that it's a lot easier not to create in a vacuum.Speaking only for myself, I find it creatively stimulating to have other people's setting elements to work with and around. But then, I've always had a crippling fear of the blank page.
Obviously, a point of concern.My fear of allowing these easily created zones is a lack of cohesion to the world. The prescribed norm would be to create your own zone for whatever new purpose you come up with.
"The sundering minor Its legions flush with seemingly endless goblinoid hordes the Imperium had engaged in a long period of expansion; growing to dominate more than a dozen isolates at the height of its power. Virtually every goblinoid of fighting age had enrolled in the legion forming a devastation force that rolled across the cosmos; which left their own isolate vulnerable to an invasion. Unwilling to give up their fertile newly claimed isolates, which had already been divied up, the Senate dithered, bickering over which legion should return. In the end the goblinoid isolate was completely overrun, and connected as it was by carefully engineered shifts to key points in the system the whole Imperium was vulnerable. Goblinoids, in many case freed by their officers (who were themselves goblinoids after years of bloody warfare had taken its toll on the eladrin offier core) broke ranks; streaming back to defend their homelands and families. Concerned about the threat to the entire empire the senate authorized an awesome magical ritual, the like of which had never before been performed in the history of the Imperium, coordinated across dozens of worlds; officially the explanation is that this ritual would "temporarily close all shifts into the goblinoid isolate" giving the Imperium time to muster forces and launch a coordinated counter attack. What actually happened can only be described as a catastrophe. Under the pressure the the goblinoid isolate simply broke; the isolate fracturing and disgorging its contents into all the planes and hundreds of isolates. While small bands of survivors would survive most of the goblinoid population, million of beings, were wiped out in an instant. The Senate attempted to put the best face on things, but an unfortunate word by a shocked arcanist on the Senate floor would give the event it's name... the sundering minor."

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.