The North East of England has a lot of links with the Rhine-Ruhr, and Dusseldorf is the largest airport on that region. Both being industrial regions, a lot of Geordies went to Western/North western Germany in search of jobs. I'm surprised we haven't seen a return of the Hanover route or a route to Hamburg. I reckon Hamburg would be a good shout for Ryanair.
Fingers crossed EZY and FR do have something in store for us, personal wishlist would be
Ryanair: Hamburg, Riga, Budapest, Ibiza, Chania, Rome (CIA)
Easyjet: Amsterdam, Paris, Milan (MXP), Venice
I'd be happy with Bergamo from FR but I think EZY would be better for attracting business and leisure.
Catania or Lisbon would be lovely, welcome additions but less likely
A London route (LGW/STN/SEN) would top it all off perfectly
Good news about Eastern to BHD, is it still just x1 daily? x2 daily would be better but I think that's a wise decision from them and will hopefully lead to more from them in this regard. I can't imagine IOM bound pax being all too inconvenienced by a quick stop in Belfast... Less so than BHD pax having to go through IOM anyway