I'm still not sold on the idea of the HSTs limping on into their 5th decade, but if this is going to be the case, I think GWR have missed a trick by not branding them as HST GTis. HSTs are probably one of the few trains the public could identify and most will know a GTi is a faster more powerful, better accelerating model of a car, they could market the 'new' trains as a 'modern classic reborn' along the lines of a Peugeot 205 GTi.
They could even get a few suitably lairy graphics and some slick marketing may well drive up custom.
Instead they've been labelled 'Castles' which no one bar train wonks and people over 80 will know or care about.