Dream ONYes Okehampton Should be back on the Railway map, but it's not going to happen.
FGW▸ could do it but they are loosing money hand over fist, with far too many managers, with bad train crew rostering, the massive use of contractors, (who are there to make as much as they can out of FGW), etc
SWT▸ could run a very limited service Early and late to/from Okie on the back of the first and last trains of the Day from Exeter S D to Waterloo.
The owners of Dartmoor Rail could if they can get around Hugh Loops run a service to Yeoford (Rebuilt Downside platform) and make connections to the Barny Exeter trains
But 90% of would be passengers would be lost because of changing trains Better for Dartmoor Rail to build platforms at Coleford Junction.
The best hope for regular trains to Okie would be Open Access but that would need services run from Okie to London, or Birmingham, Manchester etc, where most revenue would come from the Rail Settlement Plan ie pick the pocket of FGW by running trains to London

Yes I know there are NO spare paths for trains to/from London, but then there were no spare paths to/from London KX for Grand Central. Somehow they run!