Existing season ticket prices are constrained by long standing political imperatives. The southern portion of HS2 will form an entirely new route that runs in parallel with existing routes. There will be no existing user base that needs 'protecting'. If seats can be filled at peak times with passengers paying, say, £300 return for Birmingham to London (which wouldn't surprise me in 2026/27), everyone should pay close to that price. The only reason why season tickets should be offered at a modest discount compared to the daily fare is if the calculation is made that this will encourage repeat travel and generate more revenue overall.
Thanks to a variety of efficiencies it would be cheaper for the state (which is the ultimate guarantor of the entire rail industry anyway) to provide a seat to a season ticket holder from Birmingham international to London on HS2 than on the Classic line system. Forcing them to use the classic line would have the effect of increasing net subsidies.
Therefore there is no reason to withhold season tickets from HS2 traffic, certainly not until the line is rammed full at peak times.
The capacity of the line is so enormous that £300 tickets would not be able to fill it.
In the two hours to 10AM something like 40 trains, each up to 400m long with 1000+ passengers will be arriving at OOC/Euston. [And a 400m double deck could plausibly have 1100 Standard and 250 First class seats]
If train operations start at 6AM you could have 80 trains arriving if you start trains short at Birmingham and Birmingham International to use the early morning southbound core slots.
You really think there are 80,000 plus people willing to pay £300 per day, every day? Plus standees ofcourse.
If the cost of commuting from Birmingham to London on HS2 is, say, £1000 a week, I would not expect HS2 to suddenly turn into a new London commuter route. There is no political imperative to subsidise rich London commuters on a new multi-billion pound taxpayer-funded rail line.
There is the political imperative that it be seen to be a success.
Which means it has to be running full.
And I don't get what is so horrific about standing on trains? Rail accidents are so insanely rare that it makes little difference - especially as passengers are not in any way restrained anyway.
And you aren't subsidising them if your line isn't full - because the marginal cost of longer trains when all the infrastructure is already in place is very very low indeed.