I disagree. A through station doesn't need all the platforms that a terminus does, maybe 2 per direction, if most trains run through or just out to a reversing siding for the terminators.
Two per direction would still be four, you'd be looking at something like quadrouple the station volume of a Crossrail station to do that.
It's only 1 station per conurbation (rather than the 1 per suburb or Council, or whatever it was that Crossrail put in to buy them off.) No need for platform screens and doors, just a part of the InterCity network.
Platform screens aren't going to significantly add to the cost and would provide major improvements in reliability and passenger control. I doubt you would eliminate them from the design unless you were truly desperate.
We built a good new underground in Liverpool 40 years ago, why can't we do 2 stations in Brum and Manc now? Tunnels are cheap compared to surface lines in urban areas...
The total volume of the new construction underground railway in Liverpool in the 1970s probably adds up to less than the volume required for one of these proposed stations! It's a really small scale system compared to what would be needed to make an underground HS2/NPR station work.
p.s if OOC only needs 6 high-speed platforms (
https://www.hs2.org.uk/building-hs2/stations/old-oak-common/) and northbound services are going alternately(?) to Brum and everywhere else in the N how on earth can HS2 Brum and Manc possibly need "five or six 400m platforms at minimum?"
Well if we are building a high speed transpennine line you will be running quite a lot of trains through it.
I don't think it would end up much quieter than the Core section
The original Y-scheme plan is 3 trains per hour each to Manchester and Leeds, then something like two more London-North East (beyond Leeds). All those trains will be routing via this underground station. So that's 8. Although those trains will all be calling at the same stations in this scheme you will need that many for capacity anyway.
Add in the proposed 4 trains per hour Liverpool-Leeds/North East, which takes us to twelve.
Then two more trains from Birmingham-North East to relieve XC etc.
We've reached 14, which isn't that far from OOC's 18.
Certainly I would be nervous about going below 5 platforms (2 each direction with one in reserve).
Maybe the argument for a through station in Manchester would be different if a through station suitable for 400m trains was also proposed at Leeds, but that’s not the case.
Not immediately, but Leeds can and has absorbed 312m long trains before (GNER 'White Rose' services using the North of London Eurostar sets). It is certainly capable of handling trains much longer than 200m as it does it every day!
Just because Leeds will not be receiving 400m platforms immediately does not make it a good idea to permanently limit trains over the Transpennine line (which would defacto become the main London-Leeds line) to 200m trains. That would be a terrible plan and squander capacity worth tens of billions of pounds!