Good as they were in the day, I am totally confident that Jason and the crew will develop a better Mk3 than Jouef produced.
Cost wise, there will be no expensive problems with the tilt reproduction, as it was not a tilting train, and whilst the carriages had BT5 vice BT10 bogies and a different electrics/jumpers, the detail differences should mean that it will be possible to reproduce 1x power car body, 1x 1st class coach body, 1x 2nd class coach body, 1x TRUK Kitchen car body, 1x TRSB restaurant/buffet catering vehicle body; the other differences being largely cosmetic in a model, and not particularly difficult to reproduce in 4mm. And no cheese butties to wedge under doors. Paint differences and a second power car, being possibly as a dummy, could be purchasers' own choices.
Those worrying about cost are probably not going to have to worry too much, plus there is likely to be a lead time for these to be produced, meaning diligent saving over the next say 12 months will allow a version of the train to be obtained.
My one plea to Jason is:- like the APT-E, make it without compromise, (in fact, with less compromise as it doesn't have to tilt), and ensure that it is once again P4 compatible.
I will be looking like the APT-E, to recreate the complete 1973 train...