Germanwings is no longer the airline it used to be 10 years ago. It has a differentiated product and also code-shares with the likes of LX and OS. In fact, it also provides feed to UA to/from LHR. So it is possible that BD can work something out if it thinks connecting passengers are needed to make it feasible. Not sure that it is indeed needed, given that MAN and BHX have 7 weekdaily flights to DUS and apparently up to 600 seats a day to DUS are filled from those destinations.
As others have said, DUS has a really good network of UK destinations so there appears to be a market: GLA, MAN, BHX, LBA, NCL, LGW, LHR, STN, LCY plus seasonal flights to JER, GCI, NQY, INV, EXT. In the past, there were also flights to EDI and SOU, and destinations like NCL and GLA are, as far as non-LCCs are concerned, an exclusive for DUS and not served from MUC and FRA.
This could, of course, also mean that "QLA" is a filler for another UK destination and not for BRS. EMA would be a possibility, given that nearby CGN was served from there by various airlines in the past and BD has an aircraft based at EMA anyway. Guess we will just have to wait and see.