A new railway connection that is likely to be very busy and popular - how can that possibly be a bad thing?
Carterton, poplation 15,000 would have to be served too.
I must admit when looking at the map it does look odd that the Witney Line ever shut. However it never had more than a handful of trains a day, and I suspect in the sixties the buses just zipped straight into central Oxford before congestion took hold
If you did it the logical thing would be double track to between Eynsham and Witney then single long siding with stations at Eynsham, Witney and Carterton (terminus). The flatness in the area makes new alignment feasible.
Logical thing to do would be to extend the Padd - Oxford terminators along it. You would of course have to electrify it. Would imagine that a new Witney station alongside A40 would have immense parkway potential as another poster suggested.
That said, Hanborough is clearly Witney Parkway in all but name (direct route along A4095, with virtually all trains stopping there now, hourly bus from Witney journey time 21 vmins, and car park stuffed to the gunnels with cars on every nearby verge on the A4095 on the google maps streetview photo (I recall it used to have about 2 trains a day like Combe and Finstock) and I suspect much of the traffic on a reopened Witney branch would be abstracted from the Cotswold line stations so whether it would improve revenue much is another matter.
It looks to me like rebuilding Hanborough as Witney Parkway with a very large car park and the no.233 bus service increased from hourly to half hourly between Witney and Long Hanborough Station, with evening services, would be a more realistic option.
To be honest some serious renamings on lines like the cotswold line would help get some towns on the rail map:
eg
Radley - Abingdon Parkway
Hanborough - Witney & Eynsham Parkway
Charlbury - Charlbury & Chipping Norton Parkway
Shipton - Burford Parkway
Kingham - Stow Parkway
Suprised Shipton has so few trains, I thought most trains used to stop there.