Germany's leading broadsheet FAZ today runs an longish article on DUS and Jet2 is explicitly mentioned as one of a number of new carriers that will benefit from the recent decision by the state department of transport to increase the number of slots.
A LBA-DUS route has been looked into a couple of times in the past. BMI has repeatedly requested slots for LBA at DUS in the past. There should be a market, given that LH and BA both have a couple of daily flights from DUS to MAN.