The current railway system is already there, by expanding it your using less ground(I.e, ground which more often the railway already owns but has no sue for) and disrupting less peoples lives, for example Bristol TM to Parkway quadruple track was done without doing much damage, as is the retunelling of Kings Cross. HS2 has demolished peoples homes, they've cut down trees without prior permission and destroyed a lot of habitat.
All i'm saying is for the benefits it will bring which are so small, is it really worth it, we need our current railway to be brought up to standard not making new lines to take over demand. Look at HS1 it's mainly for people who can afford the fairs, otherwise your stuck on a normal South Eastern train.
In regards to GWML, Bristol, Reading and London have received massive amounts of money, further West we haven't, apart from the rebuilding of the sea wall in 2014, and the current proposals around Dawlish/Teignmouth that nobody locally want's. The Heathfield route is the best option as the ground to Bovey Tracey is already there and it would leave and rejoin the mainline in between two of the main stations on the route. The Okehampton route won't happen as it has too many challenges and is far to expensive.