I rather doubt that there would be many branch lines for the D78s to run on anyway, almost all of the TV branches are to be electrified and most of them will have platform extensions or modifications where necessary carried out to allow 4 or 8 365s. The only branches in LTV that would be likely candidates for the D Train would be the Marlow - Maidenhead and if little interest is shown by TfL/Chiltern, West Ealing to Greenford. Class 165s will be covering the Metro West area while Class 150s will be covering the branches in the West of England.
No, but it wipes out the possibility of incremental extensions based on beating the target.
The DfT definitely wanted to go further (with the same money, of course).
Interesting I know there has already being mention of some Battery 387's, I wonder what the alternative Rolling Stock solution is for Portsmouth - Cardiff is, HST's perhaps? and is the motivation behind this to free up some 16x for TPX?
An actual potential use for the Vivarail units is interesting, and FGW do have a number of branches which are relatively short and fairly low speed and the 150/153's etc. could be used elsewhere.
10 387's to leave Thameslink March/April 2016, the 8 new ones delivered start of 2017, IEP to have more standard and less 1st than the draft layouts perhaps not entirely surprising given the recent 1st class reduction.
I don't think that is necessarily so. The economics of wiring beyond Newbury will be completely different if they do Southampton to Bath in a few years time, either beforehand or simultaneously. Also affected by any decision to do the XC NE/SW axis...