The interesting question is whether or not BACF would indeed use that aircraft for a DUS route. The Duesseldorf market was served for quite some time (1996 to 2010?) by VLM, EAE and Lufthansa with cheap-to-operate 50 seater turboprops, but apparently was never a real money-maker. Not sure why BA is interested if even Lufthansa was unable to make it work with a smaller aircraft.
The other question is if a spare E170 would be needed for IOM if BACF is interested in that market in the long run - I guess a few pax now travelling on BE from IOM to London will be uninterested to move their business to the big red orange which will be the only alternative once BE is gone,