For this reason CGN will not work with a 737 too many passengers.
Oh, why are you rubbishing this before they even run it ? Sure, it was tried and failed 4 or more times, but looking e.g. at later FR HHN-BHX's, that was pretty popular just before they stopped it (I think they send this aircraft to Venice now - HHN is quite focussed on Italy and Spain these days), weakness of the GBP surely played a role. 4U's MAN-CGN didn't seem empty either, depite a good coverage of LH and BE to DUS, it has very similar flight times as the new BHX-CGN. Though DUS seems close to CGN on the map, many people south of CGN I think prefer to go there if they have the choice. So I with them luck, welcome back Koeln/Bonn