The £ v euro, Brexit and new future routes from BFS could cull the numbers significantly.
You seem to have an illusion that people drive to DUB just for the hell of it!!
Can I assume when you have Brexit and cull numbers traveling to DUB in one line you are referring to the fact that people in NI will be worse off economically hence the drop off. You are not that naive to think Brexit will deliver lots of new routes from BFS, Current £ value is bad for Ryanair and if it gets worse well who knows...