The EDI route initially had excellent loads on Fridays and Sundays, virtually full. Mondays and Thursdays were OK. Tuesdays and Wednesdays were dire. It was operated in the middle of the day though so wasn't particularly useful for business. There wasn't a Saturday service until later on, by which time the midweek flights had been dropped. The schedule change echoed the BFS timings, and encountered the same problems. The early outbound flight on Mondays and Saturdays had dire loads but the inbounds did OK. On Thursdays, Fridays and Sundays it was the reverse as the flight operated in the evening. The outbound flights were quite full and the inbound which arrived into SEN late not being so popular.
What we don't know is how the route would have performed if originating in EDI with a proper morning and evening schedule removing the issue of first/last trains. Perhaps if EZY ever abandon the STN-EDI route it might be something they could consider.
In principle I think there would be enough local demand for Stobart to operate say a Mon/Thu/Fri/Sun schedule to capture the weekend market. Without knowing the terms of the Flybe deal I'm not sure if that would be permitted beating in mind BE operate LCY-EDI.