Interestingly Worcestershire County Council's Rail Strategy identifies the Manchester - Bristol as the service they think it would be plausible to have call at Worcestershire Parkway.
The Worcestershire Local Transport Plan focuses on attracting and supporting economic investment and growth, by delivering transport infrastructure and services to tackle congestion and improve quality of life.
www.worcestershire.gov.uk
They identify that service, presumably as the one which represents the path of least (but still significant) resistance with CrossCountry. The strategy goes on to talk about additional services between Birmingham and Bristol/Cardiff calling at WOP, which I suspect is probably the most realistic way of achieving more calls.