Advantage to a move? Let's pretend Belfast and its immediate environs are the economic hub of NI. Let's pretend it is also the political hub of NI. Let's pretend people who fit both categories live nearer BHD than BFS. Let's pretend there's a premium world class service allowing these people an extra 30-60 mins in bed compared to EZY/FR from BFS, and they keep flying to LHR. Let's pretend some of these people fly BHD to LCY at a much higher cost than using the competition at BFS.
Let's pretend in total these passengers amounted to 10s (no need for an apostrophe on the plural - Queen's English and all) of thousands of people. When you engage reality, I STILL see no business sense in moving to the shed.