I dont Know, look at it this way:
-KL used to serve Sheffield City, so they must see demand from the area
-They serve LPL/MAN BRS/CWL EDI/GLA so HUY/DSA is not totally inconceivable.
-They rely on connections, not just O&D so they have 2 ways to fill the cabins. Easyjet had good loads DSA-AMS, so surely this combined with a smaller F70 could work 3 times daily from DSA
-They serve LPL/MME so obviously have a good relationship with VAS, and that could be exploited to bring them to DSA.
Other than that, what about AF for the same reason?
They dont serve LBA, so the connections through CDG could work. They also have the ATR72 or the E190 so the right sized aircraft for the route. They are also part of the AF/KLM group so another good reason.