Well Pan... I would suggest that if the current model exits then margins will be tight at both facilities, thus no real investment at both apart from little capital projects here and there within each facility. Thus stagnant!
What I would like to see is BHD closed and turned into a useful urban space - which would make much more money for the current owner than what is on offer at present. It would also improve the well being of 10,000s of folk living under the flight path at the moment.
BFS would have to accommodate 8m passengers per annum in the current climate, thus would have to build a proper facility to cope. Public bodies would have to invest in infrastructure to and from the airport. Everybody happy! Belfast would become a normal city within aviation terms for the size of its market. Until that happens stagnation will be the norm.