> As someone who spent a lot of time in London I hope he is correct about the track capacity released for local trains once the intercity move to the new lines.

Well of course there is. There's currently 10 trains an hour in each direction that run non-stop through Milton Keynes.

There could easily be an initial service along the lines of

Slow lines

  6tph London-Harrow-Watford-Stations to MKC
  6tph London-Watford-Hemel-Leighton-Bletchley-MKC

Fast lines

  6tph London-Watford-MKC-Northampton
  4pth London-Watford-MKC-Rugby-All_stops_TrentValley-Stafford
  4pth London-Watford-MKC-Rugby-Coventry-Airport-Birmingham

And I suspect stops at OOC will come too.