I assume (perhaps wrongly?) that the refurbished Class 373's will be fitted with ERTMS▸ for use somewhere on the UK▸ network; would the WCML▸ or ECML▸ really be superior to Brunel's masterful GWR▸ ??
I think that yes, you do assume wrongly. There is no evidence whatsoever that any 373s will be made available. The Eurostar order is not a replacement, just a small addition to the fleet, indeed the existing fleet are to be refurbished for continuing use on the existing routes.
The completely separate
DB» order is for additional services to be operated to new (German) destinations - so it too has no bearing on 373 availability.
2. London Underground is already introducing platform edge protection to prevent "incidents"; is there now a similar role for 125+mph lines ?
Platform edge doors were not introduced to 'prevent incidents', but to aid with station ventilation and deal with the 'piston effect' of the trains pushing hot air around the tunnels. The more obvious safety feature (as far as the layman is concerned) is actually just a beneficial side effect.
Paul