I think if it is done in a way similar to Rilla's it might work. The main GM runs the main story line, while the other or co-GM runs a concurrent story line that ties into the main story but with different characters. It would be like LoTR when the party breaks up, the main story line continues on with the main GM and the secondary story lines runs with oversight by the main GM and co-GM communicating so that the theme consistency continues. 

In fact I would run a multiversal event with Rilla since I am comfortable with his storytelling ability that if we did it, the overall story theme would continue while two separate stories ran concurrently perhaps even overlapping at times.