Rumours have surfaced periodically about a jetstream operation from Coventry for the last couple of years without any firm details.
Although Southampton and Bournemouth are served by a good train service from the Coventry region, Exeter and Plymouth are not you have to go via the dungeon called Birmingham New Street which is a real pain and time consuming. I'm not sure that a service already on offer from Birmingham or perhaps more pertinently East Midlands automatically rules one out from Coventry.