Certain GM-styles attract and repel certain players. There'd need to be at least some overlap for it to work. When I was in Kadaeux' games for example, a big deal was that players controlled a ton of NPC's and had a dozen of resources to manage which gives them the freedom to create and pursuit their own character arcs (albeit within a system with a number of dices.) A lot of my players in the Library would likely be confused with such a style. Meanwhile, for the Library I like to work with smaller, more intimate scales which focus more on putting down one-at-a-time challenges to tackle, which might make people who flock to Kad's games feel limited. We'd both just be working with storytelling posts, but the implications made by these go beyond the writing style. If our playerbases were the same, they'd probably be able to switch without a hitch, but because they're so different it'd take a lot of trial and error. Past what I think is doable in a few weeks. 

I think guest-GM'ing would require a certain amount of overlap in style. You wouldn't let a free GM randomly switch it up with an advanced GM because their players have completely different expectations. With storytelling posts you give your players. besides plot, a certain amount of space and a number of expectations. Familiarity, as mentioned before, would also be a huge boon. It could work and I agree it could be interesting, but I can't help but be kinda sceptical when I try to come up with concrete examples.