Probably just JetBlue. The main purpose of T5i is to allow JetBlue to clear international arrivals at its own terminal, instead of having them arrive at T4 and towing the aircraft over to T5 for departures as they do now. It will make things much easier for international-to-domestic connections. They might consider allowing partners in on a one-off basis as opportunities arise, like HA and EI, but I don't think adding other carriers is the primary goal.