I would be gobsmacked if we ended up with services exactly as I wrote in that fictional piece ... interesting, I found someone else's view on how the railway system (elsewhere in the world) will be in 2032:
http://www.nzetc.org/tm/scholarly/tei-Gov07_02Rail-t1-body-d15-d5.htmland a possible 2031 route map for the Oxford / Milton Keynes area:
http://www.eastwestrail.org/downloads/Maps/schematic_milton_keynes_south_mid.pdfPopulation development won't - I don't think - be in proportion right across the South West; it's certainly not planned to be that way and as this is "fresh air" speculation, there are some more (and some less) likely things in there. The regional Portsmouth to Severn Tunnel service goes via Gosport and Eastleigh to keep journey times sensible ... (and there are some other fairly controvertial changes that you haven't highlighted too, Tom!)