I think there is just much less demand from Manchester to Birmingham than to Leeds overall. They're just not as connected.Manchester might grow to 4 tph to London, even to Birmingham too, but that would be on HS2 rather than the WCML. Basically if the capacity at the HS2 stations at those three cities exists due to the eastern branch not being built, I suspect that over time we will see their frequency grow. As an example, today Leeds to Manchester has 4 fast services running at about 50 mins plus a number of slower services. Post HS2, Birmingham to Manchester will be faster than Leeds to Manchester is today and if the capacity is there I see no reason why frequencies between thise two cities wouldnt be on a par with Leeds-Manc today.
4tph WCML to Manchester was once looked at, would have made it 2tph from Wilmslow, also Crewe and probably Stafford and/or TV. But not needed for London-Manchester alone. So it's aggregate demand, which HS2 (captive especially) doesn't do so well. Hence my suggestion of rejoining the trad lines a little sooner to soak up some other journey pairs and demand.
Maybe in time it will all be viable. Would seem for now that we don't need as much stock (or OOC platforms!) - for now.
