In general, I agree with the observation re German domestic flights. However, a window of opportunity could open once TUIFly has disappeared as a serious competitor as a result of the planned co-operation with airberlin. I guess much will depend on how much effect the growing number of Ryanair's domestic flights have on the domestic travel market that, until now, is only served LCC-wise by TUIfly and Germanwings (although in all honesty, airberlin and Lufthansa are not much more expensive if flights are not booked a year or so in advance).
I think easyjet's biggest problem is that they do not have a serious base in the Rhine-Ruhr area which is the largest European conurbation. DTM did not work out, they shied away from CGN because of TUIFly and Germanwings and apparently they are not patient enough to built up a presence at DUS slowly by adding flights whenever slots become available.