Gloucester and Cheltenham are fairly small on their own but they are only 8 miles apart and if you put them together there's 1/4 million people (and there's the transport links).
Local pax have always been in the mindset to use BRS or BHX but I think this is changing..... allegedly Manx2 affected Easterns loads into BRS so they dropped the route.
It could probably sustain routes to DUB, GLA or EDI and if the RESA reinstatement happens you could see WOW, Arran or FlyBE having a look.