Quite, all this talk of extra coaches, electrification, etc. for the Chiltern line would help, but not by very much.
Currently there's 3tph London to Birmingham on the WCML, let's assume that they have 1,640 seats (so a 9 coach 390 and 2*11 coach 390). To provide a 50% increase in seats (820 seats) by providing extra coaches would require about 12 extra coaches with 70 seats in each on the Birmingham services.
However what do you then do to provide the extra capacity for Manchester? The simple way is to remove trains from Birmingham on the WCML and divert then to Manchester, however that would then require even more coaches being added to Chiltern services. Let's say another 10, so that's a total of 22 extra coaches on Chiltern services. Could you even for in that many extra coaches to Chiltern services?
However Coventry has gone from 3tph to 2tph, which is something that those opposed to HS2 would say wasn't acceptable.
Whether it's a strategy for Chiltern to lengthen their loco hauled Silver Sets by adding coaches later I dont know? It's not a bad idea. Would it possible to have 7 car sets?
Coventry might remain to be seen. The service spec is only the minimum isn't it? And what if LNR end up getting the chance to use the fast line south of Rugby once HS2 opens? There wouldn't be too much of a loss imo.