If the job includes initial pilots being based at Cologne I don't see how someone could consider not relocating - at least initially. Perhaps you would have more flexibility after growth when additional domiciles should pop up.
Should be interesting to watch JetBird start up. I am curious to see how they do in this market. I guess if you can afford the switch and you don't mind a little risk, it sounds like a fun job and a nice aeroplane to fly. I wish them luck!