As a Didcot (home of the 'Diddies') resident, I can confirm what Oxford Don is saying is more or less right. Oxford want to own their stdium, they will never move out of Oxford.
With regards to commuting to Kassam stadium, I have never had an issue getting to or parking at the stadium. Traffic can last up to about 10 minutes on a match day, with most traffic building up at the junction near the business park (these guys dont let you use their parking grounds....pr*cks). The overflow park behind the vue cinema, is more than adequate and is never usually full.
As for Didcot, the stadium is in the centre of lady Grove estate with easy access to the grounds. 8 quid entry fee, a pub and shed that sells lukewarm tea. Proper Diddy team!