According to SpaceX on 20 Sep: "SpaceX has nearly 50 missions on manifest to launch over the proposed 5 year lease period and we can easily make use of the additional launch site. At the time we submitted the bid, SpaceX was unaware any other parties had interest in using the pad. However, if awarded this limited duration lease on 39A, SpaceX would be more than happy to support other commercial space pioneers at the pad, and allow NASA to make use of the pad if need be."
"[Blue Origin] has not yet succeeded in creating a reliable suborbital spacecraft, despite spending over 10 years in development," Musk wrote. "If they do somehow show up in the next 5 years with a vehicle qualified to NASA's human rating standards that can dock with the Space Station, which is what Pad 39A is meant to do, we will gladly accommodate their needs. Frankly, I think we are more likely to discover unicorns dancing in the flame duct."
Congress Voices Support for NASA LC 39-A Leasing, earlier post