EGCA,
1,160m was put in for DHC8's, before 1,160m the two PLH runways were circa 800m with one of those being circa 50% grass. Scheduled services, Islanders, Twotters etc, operated from PLH when it was grass, DHC7's joined the party once there was circa 800m of tarmac and DHC8's joined once there was 1,160m.
For how long has Staverton had grass and/or had 800m or more tarmac? PLH would have already had quite a significant route network at that stage, LHR, LGW, ABZ, EXT, NQY, BRS, ISC, JER, GCI, MXN, BES, ORK etc. so if it already hasn't happened for Staverton then I'd guestimate that it's not going to happen, well not anytime soon anyway.