I can't imagine it would be popular to cut the Chiltern service to Birmingham, which seems to have been very successful, in favour of a slower and more indirect service via Oxford.
The only reason it has been popular is because the privatised industry has been charging too much for the fastest services between London and Birmingham. This is entirely in line with government policy and is exceedingly unlikely to change.
However, there is no reason, in the strategic and long-term sense you are talking about, for anyone travelling between central London and Birmingham city centre (plus a sizable chunk of the West Midlands, and places like Shropshire and North Wales where Chiltern sell tickets to) to do so via High Wycombe. This is the only reason it has been succesful. It would be much better to take all of those passengers away and have them travel on the WCML and use the Chiltern Mainline to serve Buckinghamshire and Warwickshire, and anywhere else where journeys to London Marylebone are the fastest way to central London.
Should Chiltern be told to end their services to Oxford?