As per runway length, with the 1500 or so licensed they might not be able to use fully laden 737's, but the more regional sized aircraft operated by the likes of Flybe would presumable be of little problem?
I imagine though that the current show stopper would be the fact that the apron is way waaaay too small to handle much more scheduled stuff than it already does. A significant extension would have to be completed before a (much needed as you guys rightly say) runways extension would be worth the cash?
Also, I don't know what you guys think, but the airspace around Oxford seems pretty congested, would this have much of an effect on their plans for expansion? E.g. with the Brize Norton MATS intersecting the Runway 01 extended runway, surely some major airspace re-arrangement would be necissary to make Oxford a really busy jet-traffic runway?
Also, I wonder what effect all the local drop zones would have on Airline safety cases...