If FR did land back at BHD with 1 or more routes id say the airport would struggle unless there was serious expansion. I'm Sure they could create additional stands easily but the main terminal is bursting at peak times.
the check in hall has limited space
security search is tight for space as it is
the departure area has hardly enough seating as it is
FR flights bring big paxs numbers hence the attraction as these paxs will spend in the airport.
for sure i will fly with them whichever airport they fly from, if indeed they do return to Belfast. Im hoping for European flights. Fingers crossed, no more driving to Dublin to get to my usual destination currently not served directly from BHD or BFS.