DUS is Germany's 3rd busiest airport after FRA and MUC and covers an 11m metro area with excellent transport links and lots of commerce and industry. If the state of North Rhine-Westphalia was a country, it would be in the global top 20 in terms of GDP. A BRS - DUS route would be an interesting proposition. It is fairly close to Frankfurt (less than 1.5 hours by direct high-speed train), but I think it could still work, there is enough 'mass' there (unlike, say, Hanover). Not sure how much bmir's routes are really driven by pleasure, I would imagine that for city breaks and VFR the pain threshold is much lower than for business travellers when it comes to fares. The question is would it work without the extra transfer passengers feeding into a hub (not sure what status DUS has for LH these days or if it's any good as an LH hub, ignoring Air Berlin for now).