Compared to an open field that cows normally graze in, the Kassam is quite good.
It has awful parking, even worse access. Walking, it would take me close to two hours to walk to from the railway station, but I wouldn't be able to walk that far in reality. A fit person, maybe an hour and a half.
The ground isn't designed to keep rugby balls, so I can see cars getting damaged every week. All of which could be managed.
OTOH. A new ground next to the Oxford Parkway station and park & ride would be an excellent option. The fields around there have been decimated with aggregate workings, so might make an attractive 'fix'.
But, what then do you do with training centre? The ground would be an unworkable distance away.