I mean you're never going to get the loop at Whimple for service resilience alone, so the enhanced service has to be decided upon first. Its unlikely they'll be much appetite for another train per hour through Central, and Wellington and Cullompton are more likely to be served by the Penzance Cardiff services. So the Barnstaple or Okehampton being extended is likely the best thing to do, although like you say rolling stock is required for this. Mark Hopwood made a point of saying that there would be no new services (this was in an article about the proposed Newquay to Falmouth services) introduced whilst the fleet size is being shrunk to meet the governments targets on reducing costs.There are lots of talks about extending the Barnstaple/Okehampton lines to cover the extra service, but surely (in the medium term future) it would make sense to create a new hourly service, that would run between Axminister and Taunton (maybe extending to Bristol?). Then, the new Wellington & Cullompton services get regular services that go to EXC, and places on the WoE line get an frequency increase. You could in fact have the Waterloo services skip Fention, Whimple, Cranbrook, and maybe Pinhoe. This obviously would require the passing loop at Honiton, and probably some extra rolling stock (project churchward?) and staff.