The whole idea of this venture is to try and prove to airlines that SEN is a viable London arrival airport, especially on the city routes.
If Stobart do succeed, then it would demonstrate to other carriers that SEN does work and therefore they might consider flying from there too.
Although normally you wouldn't want a shared airline/airport venture, in this particular case it is a logical idea which could pay off in the long run.
AirportPlanner1 Humberside Airport is owned by Eastern Airways, and you are correct that they do provide holiday charters.