So another argument is that HS2 will
"increase commuter capacity"

Humm well it will be like Concorde across to the states, yes it increases transatlantic capacity, but at what cost to the customer? Lets say HS2 is built now & you live in Birmingham, its same story if you live in Manchester or whatever further up line. Say that's also built.
Standard journey time is 1hr 24 mins to London from Birmingham, on West Coast. Chiltern's new mainline services do one in 90mins, which is non-stop.
Virgin also do a quicker 1:12 morning commuter special service, which is their quickest. HS2's time will be? 49 mins.

So it saves a whole 23 mins
/engage sarcastic voice
woooow
/disengage sarcastic voice
Its going to be a fact, that the fare price will be
significantly higher than West Coast or Chiltern. At least 25/30%, HS1 proved this, as their fare prices are higher than standard services and high speed services have been
reduced since it was completed.
Lets look at it from other foot, you commute to London for your job, so you are a "commuter". Would you pay £600 a month to get to work, or by paying £480 a month? I could save £120
per month, by getting up 20 mins earlier? For as single man thats a no brainer, also if your married with kids, thats a considerable amount of extra spending cash.
I used to commute from Bicester to London every day via train for several years, in the end (2009) It cost £360 for the ticket, £420 if I wanted tubes zones and £480 with car parking included.
I dropped tube and cycled to save tube fares, as do many others. People will not pay the premium to commute on HS2, only the few which are allowed to expense. Which will basically be first class customers from current services...
All we will have is a slightly faster service, with some very empty trains....