In a previous interview WPS said that if FRA got an additional runway there would be oppertunities for Regional to operate from a number of regional airports to FRA. There is, however, only so many passengers who want to fly from ABZ, EDI, GLA, LBA etc to FRA. I guess the frequency would reflect demand.
The new runway (~ 9,000 ft) opens at FRA next year. And I don't consider FRA as a particularly appealing destination either, but BMI Regional could become a real competitor for long haul destinations from the UK regions if they had a organised feeder system through FRA. Right now, if you have a choice at all, you're usually looking at BA through LHR or KL through AMS.