Either way the overseer counts as the GM, doesn't he? I'm not sure how that would work out, but we'll see I guess.
We need to discuss it and acheive some kind of unity on it. Like what are the duties of the GM? And even if we actually need a GM? And if GM and overseer is the same person or not?
These questions are perfectly illustrated with the mechanics of gods and forces: one of the main mechanics of the gods is uncertainty. Players should not know for sure what exactly certain god wants, and what does he promise for it.
There are, of course, prophets. But some prophets may be more mercantile then others, and others may be just imposters. A crafty and charismatic false-prophet could gain much power and wealth by convincing a fortress to support an unexistiing god, while stripping real gods from any power income, and thus be completely safe from divine wrath (those thunderbolts cost power to cast
).
In our old scheme GM/overseer would know the personalities of the gods, but he would keep it to him. With our new scheme, depending on election laws, a greater number of the citizens will have access to the inner mechanics of the game (because it is an overseer who actually drops a marble slab from the sky to crush the unruly prophet), and thus to the real personalities of the divines.
One of the possible ways out of this problem could be creation of an OOC council(that would collectively act like a GM), each member of which would be a proven RP-geek who vows not to use his knowledge IC. But maybe you guys have a better, more elegant way out of this?