I suspect domestic routes will be very difficult to sustain. Operator / London airport / and timings will be critical.
In the meantime, IMHO, Stobart should be on the phone to Lufthansa and Eurowings. NQY has sustained seasonal weekly service from Düsseldorf and Stuttgart on and off for a couple of years now. The south-west has serious appeal for German tourists, no reason the Carlisle couldn't do the same for the Lake District.