If FRA want to pick up more regional connecting pax and seriously challenge LHR then they need to expand the amount of UK airports that are connected directly to FRA - I think only LHR, BHX, MAN, BRS and EDI are currently connected(?) If you compare that to AF and particularly KLM, they're a long way behind. I guess that's where bmi, particularly regional, could come in, as a FRA feeder airline from the likes of GLA, LBA, NCL, ABZ etc.