There was a murmur in the news a few weeks ago that a second scheduled company wanted to operate out of Oxford and it was due to be announced last week, although clearly that's either been delayed, or was mistaken media hype..
As for people like easyJet, I see that as a bit unlikely for the foreseeable! Oxford has an award winning business terminal yes.. but a terminal with capacity for larger airline operations (forget the rest of the infrastructure such as parking) it does not!
I think before any one of the "major" airlines considered Oxford it would need a serious round of investment and probably a direct link to London too.
Phil