WRT the southern WCML:
Currently, off peak, there's 12tph on the fast lines AFAICS: 9 Virgin, 1 LM Trent Valley, 2 LM Birmingham (the other Birmingham seems to be on the slows).
Chester still needs it's ICWC service (not replaced by HS2 service). Stoke probably could do with a residual 1tph ICWC to back up its HS2 service, as well as provide places like MK with Manchester service. Coventry probably can't justify 3tph ICWC with Birmingham passengers removed, but it would still need 2tph. That's 4tph ICWC.
Given a lot of the purpose of building super-fast tracks in the West Coast corridor was additional commuter service, Northampton ought to have 4tph fast.
That leaves 4tph for Trent Valley, which is obviously overkill, but we don't have to fill all the paths initially - 2tph would be plenty.
So an embroynic plan for it might be something like:
1tph IC Euston - Milton Keynes - Rugby - Coventry - International - New Street - Sandwell & Dudley - Wolverhampton - Stafford - Crewe ...
1tph IC Euston - Watford Junction - Milton Keynes - Coventry - International - New Street ...
1tph IC Euston - Milton Keynes - Stafford - Crewe - Chester ...
1tph IC Euston - Watford Junction - Milton Keynes - Nuneaton - Tamworth - Stoke - Congeleton - Macclesfield - Stockport - Piccadilly
2tph IR Euston - Leighton Buzzard - Bletchley - Milton Keynes - Wolverton - Northampton - Rugby - Coventry ...
2tph IR Euston - Watford Junction - Milton Keynes - Northampton - Long Buckby - Rugby - Coventry ...
1tph IR Euston - Milton Keynes - Rugby - Nuneaton - Atherstone - Tamworth - Lichfield - Rugeley - Stafford - Stone - Stoke
1tph IR Euston - Watford Junction - Milton Keynes - Rugby - Nuneaton - Tamworth - Lichfield - Rugeley - Stoke - Longport - Alsager - Crewe