I'd say no. There are already semifast and fast Euston-Brum services, and the consistent pattern is a big strength. Northampton effectively does have a south facing bay - P3.
Regarding this and upthread discussion; my
reading of the strategy document (link in post 1) is that the Euston - Birmingham slow service will be severed at Northampton, with then two sections given to different operators (this presumably was written before the changes to TOCs) which might be interpreted as ensuring there is no seamless through service.
Boarding at Northampton and also hearing questions by intending passengers at New St I believe that there is a considerable number of passengers travelling between Euston and Birmingham on the LNwR services - although the ones travelling 'across' Northampton may equally be, for instance, Coventry to Watford ones I accept, but still people who have eschewed Avanti.
It all raises an interesting point, in my view. At the moment. many passengers are willing to forego the quicker transit of the Avanti services for the benefit of cost saving using LNwR. HS2 will introduce an even faster service than Avanti, but presumably (to reflect construction costs) at an even higher fare than Avanti. It seems that the intention is to remove the service with the lowest fare. Will this induce everyone to move up a price step or will they desert rail for other modes or not travel at all? I'm not sure the former will be the outcome...
Edit regarding my bold ; sorry for the confusion, the reference to the strategy document was to that in in the thread about HS2 services on the Southern WCML but these two threads do have some subjects in common. It's worth reading the strategy report to see what seems to have been decided.