I remember reading someone's post that the electric supply points in Cornwall were potentially a problem to electrification. Could Quintrell Downs be the supply point for Cornwall? Would it be cheaper for any Cornish electrification scheme to include Newquay and use this as the supply point, rather that incur the cost of a new supply point?
Quintrill Downs is the furthest west GSP on a 400kV circuit, there are others east of there that can be used to power the railway, including atleast one other that is within a few hundreds metres of railway property (at Bodmin Parkway).
There is no problem in procuring sufficiently stable power supplies, you could potentially single end feed the entire system from just the Bodmin substation but it would be far more energy efficient in my opinion to include Newquay and single end feed from Quintrell Downs.
And to the question of me comparing to the unupgraded B&H line..... there will be no significant money spent on it for the simple reason that it isn't really a sufficiently important route.
A heavily upgraded route would enable Taunton to be served via Bristol with ease, leaving only Westbury and similar places to be sized by bi-mode InterCity stock.
Any money spent on the B&H only really benefits London-Cornwall services and to a lesser extent the services to places like Westbury.
Money spent on the Bristol to Exeter line gets most of those benefits and it also benefits the XC network.