Winslow's not massive, but going by the paths in RTT from December, I think there to Euston should be doable in under an hour once passenger services start (quicker than they'd be to Marylebone if the Aylesbury branch were to proceed). 40-50 minutes to Oxford city centre (including walking time from the station) seems time-competitive with driving, and 2 tph should be attractive enough.
I don't know if it will be able to attract any people driving from Buckingham who currently go to Bicester or Bletchley / Milton Keynes instead, especially going towards London.
I don't know if it will be able to attract any people driving from Buckingham who currently go to Bicester or Bletchley / Milton Keynes instead, especially going towards London.