mart901, I think Aer Lingus Regional only use ATR72 (all 212s) aircraft, ie no 42s. Check jethros.org.uk for specific info (not sure i am allowed to quote sites!!)
BFS has been rumoured on this forum ages ago but nothing happened and the interest was about the time that EZY announced BFS MAN, so not quite sure. I think there are a few routes that could work BHX being the main one, perhaps CWL, though it would be thin. Outside of that as you say LBA, only if LS pull the route as has been rumoured. Perhaps a BRU daily 72 could work though not sure if that would be an instant hit. To my mind not a lot of other opportunities as most other points in GB well served by a Belfast airport, EMA too intense from BHD to make it worthwhile.
EI-BUD