Duo fly to 14 destinations from BHX. Of these, 3 are currently serviced by EZY from Luton (Berlin, Geneva & Nice).
Duo fly to 6 destinations from EDI. Of these, 2 are currently seviced by EZY from Luton (Nice & Zurich), one by Ryanair (Milan).
I would have thought Stuttgart would be a good route, because Mercedes are based at Stuttgart and MBUK at Milton Keynes. There must be quite a bit of corporate comings and goings from that one company alone.
Links from Luton to the Scandinavian capitals (Oslo, Helsinki, Copenhagen and Stockholm) would meet limited competition (EZY to CPH from STN). Also, since Buzz dropped Vienna, I don't think that's served from STN.
Let's hope this rumour's true.....