Whats getting me about HS2 at the minute is that no-one is mentioning links to the West Country, the line through birmingham is handily close to an underused perminant way that used to go to Bristol, now I'm not saying that it would be worth running London - Birmingham - Bristol, but...
Manchester - Birmingham - Bristol and York/Leeds - Birmingham - Bristol would be, since the're looking at running up to 4tph Birmingham - London, it could use up some of the spare capacity north of birmingham, using 'classic compatable' trains in conjunction with electrifying the cross country route down to Bristol and Cardiff so potentially...
Euston - (Old Oak Common) - (Birmingham Parkway) - Birmingham Curzon St 4tph
Euston - (Old Oak) - (Birmingham Pway) - (Manchester South Parkway) - Manchester Central/Exchange 4tph
Euston - (Old Oak) - (Birmingham Pway) - (East Midlands Parkway) - Sheffeild ?Victoria? - York 2tph / Leeds City 2tph
Manchester Central/Exchange - (MSP) - Birmingham Curzon St - Cheltenham 1tph / Gloucester 1tph - Bristol Temple Meads 1tph / Cardiff Central 1tph
York 1tph / Leeds City 1tph - Sheffeild - (East Midlands Parkway) - Birmingham Curzon St - Cheltenham / Gloucester - Bristol 1tph / Cardiff 1tph
That leaves a spare 6tph on the section from Birmingham Interchange to Old Oak Common, Add in some classic compatables to Liverpool, Preston, Chester/Holyhead theres three, you could also add some 'airside' trains and international services, but then you might want to be dropping the amount per hour on the core to birmingham, manchester and york, 3tph is not unreasonable, especially if the core route uses double decker trains.
IMO, they should do all the perminant way work for 4 track south of the delta junction, split at old oak common and not to sound silly, but the idea I read in the press about running some services on a branch to Waterloo through Heathrow is a good one. But, there should be a 'delta' junction at old oak or further out from it, so that services can run, Waterloo - Heathrow - Old Oak Common - Stratford International - Ebbsfeet - Lille etc...
or, Destinations Beyond - Birmingham Interchange - Heathrow - Waterloo
That would see 4 track from Old Oak to Delta 'north' junction, since beyond that even if most services are running to Euston, they will be at a lower speed and with closer headways to get closer to 22 - 24tph on 2track, whereas at the full speeds of the network it would be closer to 16 - 18.
Also, 'airside' trains are a good idea. It's not too hard to have a moving walkway to a train, nor is it beyond our engineering ability to be able to have luggage 'cans' (Or Unit Load Devices) also on convayor belts, and loaded onto the side of a train, on witch passengers are also travelling.
Not at all a challenge at Manchester where they can use Terminal Two and the car park space to the west, or on the other side of the M56 for the staton area, Birmingham, bit more of a challenge. Heathrow, pop it in at T5 with walkways to airside, (you have to get scanned as transfer passengers anyway), and a pepole mover can get passengers over to the new 'Heathrow East' development. Now if you don't know about airlines, there are two that operate the majority of domestic flights, British Airways (T5) and British Midland (T2/3/East).
BUT! If you wanna get passengers off domestic flights, you also need to run to gatwick, conventional 100mph line would be OK for it, but there would need to be a service, if you wanna remove domestic flights, that would run, Manchester Interchange - Birmingham Interchange - Heathrow T5 - Gatwick South.
Very quickly we're coiming up with many many servries, 4 track is gonna be needed once we're running past brum...
Also, lets not forget the intentions of Air France-KLM to replace all short haul flights with rail services, so the'll wanna be running trains between Manchester, Liverpool, Birmingham, Southampton etc etc etc. to Amsterdam and Paris CDG