Hi and great question.
First we don't limit ourselves in the long run to just one platform and our solution can work on all vacation rental platforms with not much to change.
The reason we are holding back is that there is a big enough space for growth on Airbnb only at this tie and it's better to focus on the user experience than on expansion at this stage.
Secondly we believe in Airbnb and we only encourage more people to join their platform. To give some numbers - 30% of our users are new to Airbnb completely. So we feel Airbnb will have warm approach to Superhost rather than alienate us.