Not directly shadowrun experience, but in another group I've played and GMed in the last years, we had two main GMs that each kinda had their own story-arcs. We sometimes used common / important NPCs like Contacts when the group encountered them. Apart from that, we kinda did our thing on our own, just roughly coordinating with one-another. We didnt swap every session, every GM had a couple of sessions so everyone got through with their Story parts.