Route: oxford, the villages of West Oxfordshire are in precious little danger from development, if you cared to take a look at the district's draft Local Plan, with more building proposed for Witney, Carterton (700 homes approved a couple of weeks ago) and Chipping Norton.
While I don't imagine for one minute the Chipping Norton branch will reopen - and the houses would be at the top of the hill and the far side of town from the station site - putting thousands more people in Witney and Carterton will only make the A40 even worse.
W-on-Sea, the Network Rail draft western route strategy makes clear that further Cotswold Line redoubling is a serious proposition, at least as far as Hanborough, so that woud include Yarnton junction, should one wish to revive some sort of Witney railway, whether heavy or light rail. And the formation of the branch is largely intact, though at Eynsham a small deviation south of the old station site would be needed. The biggest issues would be what you do at Witney, due to all the old railway land being developed and getting across the A40 bypass, and whether you would go on to Carterton and RAF Brize Norton, which would seem sensible.
Yes, Stagecoach runs a lot of buses, but that's as much to do with shifting the number of passengers on offer than anything else. Put on a 30-minute interval train service, shifting rather more people per train than a bus, and you would do just fine, given the far shorter journey time to Oxford that the train would deliver. Even now it is quicker to drive to Hanborough and get the train in from there than it is to brave the A40 - hence the car park extension at Hanborough filling up so fast.
Re Cowley, it's all very well talking about trams, but Oxford hardly lends itself to such things. None of the arterial roads or in the city centre offers lots of room to build sections of reserved tram tracks, so if you are using the railway formation, why not run trains, which can come from and return to the likes of Bicester, Banbury or Hanborough? I repeat, Chiltern are looking at commuting to and from the employment sites from places outside Oxford, not journeys within the city, though these would very likely benefit from the removal of commuters' cars.
And the worse the road congestion gets, the less of an issue the location of Oxford station becomes and it's really not that far from the city centre, compared with Cambridge or Bristol Temple Meads, for example.