Probably depends on how many people the game can support. If it could support a large group, we would rather have one large server. If it can't support more than a small group in the end, this might be a more reasonable solution.
So you mean like how Wanderlust-Rebirth(?) did it? 4 player/small group coop would probably work quite well.
I think the main issue is that we're trying to figure out how we can get the most return on the game / A large scale multiplayer environment was the original focus. If it turns out that for some reason that isn't possible with Game Maker we could look at something like this. We really haven't talked about this much as a team.