Balkan will not be using Plovdiv for the majority of their flights. The transfers to both Borovets and the jewel in their crown Bankso, are too long. They don't care too much about Pamporovo.
Balkan Tours (Ireland) will be using Plovdiv next year. I'm informed by their manager that the new terminal and runway will be complete and flights from Belfast or Dublin (not sure about Dublin departure) will return to Plovdiv. Hope this is the case.