If you are going to rely on that sort of equipment on the train, there is no reason to adopt a European train width rather than the greater width used for newbuild networks elsewhere in the world (Japan, China et al).
With short sections of floor raised a little over power bogies (where there's no space between the wheels for the gangway to pass through), accessed via gentle ramps. I think the requirement for distributed power jinxed this idea as far as HS2 is concerned. Girunos, like FLIRTs, have a small number of power vehicles, singly at driving ends and in pairs distributed through the train, unlike the traditional Japanese all-bogies-powered approach or the similar Alstom AGV concept which seems to have been a bit of a technical dead-end in Europe with limited orders in Italy and SNCF's continued preference for end power cars concentrating traction equipment as seen in latest Avelias such as the TGV-M, and Talgo's latest HS offerings, both of which could have provided level boarding (another spec requirement) at ALL platforms served in the UK instead of just the new platforms on the new routes.
This wouldn't have met the requirement for a level floor throughout. The full set of requirements rigidly applied have worked against level boarding outside new infrastructure, but that blindness to a lower train floor solution has been an industry-wide phenomenon until recently, and not just in the UK. The FLIRT & derivatives have been truly revolutionary in this respect, in much of Europe and beyond. In the future they might be seen to have been one of the most influential designs of the modern railway age, selling in large numbers across the world, and heralding a network-wide level boarding renaissance .
Heathrow Express adopted higher than normal platforms in the 90s. It was a rational level boarding solution for its dedicated platforms at Paddington and on the airport branch, but forced a decision on crossrail later if it was to serve Heathrow on the same tracks. At the time crossrail was being planned, there was no firm intention to replace HEX or H-Connect rolling stock but 332 withdrawal might have provided an opportunity to change the height of the HEX platforms to match the UK standard. The problem was the industry probably believed only higher platforms could deliver level boarding in the UK before Stadler came up with the UK FLIRT variant.
Plus two of them are four-rail (shared with the LU Bakerloo Line and a turnback facility).
For the Olympics, Stratford had platforms built up from Eurostar to Javelin height, so this is a very simple problem to fix.
Erm, HS2's platform height is higher than the UK's standard, not lower. So building up doesn't really work. HS2 is 1,100mm for level boarding, UK standard is 950mm platform height for 1,100mm train floor height. (Hex is 1,100mm AIUI).
We could rebuild the Eurostar platforms at Stratford to HS2 height, since they are never going to see a Eurostar.
Maybe but HS2 is never going to link to HS1 so it'd be fairly pointless. Building them up to Javelin standard is, as you say, for another thread.
