Interesting report in the Plymouth Herald.
http://www.thisisplymouth.co.uk/news/30-minute-Tavistock-Plymouth-rail-link-plan/article-732162-detail/article.html
I would like to see the Tavistock service perhaps extending to Newton Abbot thus providing more trains to Ivybridge with perhaps the re-opening of the Plympton station, thus releasing HST▸ (High Speed Train (Inter City class 43 125 units)) from stopping at Ivybridge and expanding the commuting capacity to the east of Plymouth.
Re: future plans for SW Mainline and the sea wall at Dawlish i agree that the re-opening of the Tavistock-Okehampton would not be financially viable compared to losing the link to Torbay. Therefore perhaps the re-opening of the former Teign Valley Line Exeter-Newton Abbot line via Chudliegh would be the for the best for protecting the Torbay link, but this would be complicated given the track bed has been built over in parts for the A30 and A38. Either way its going to an expensive move to preserve the SW mainline, but one that will have to be taking one day.