Really? Haven't we got a new PM who has promised to review the whole project? In view of Brexit isn't HS2 a tempting target for a chancellor trying to plug the resultant hole in public finances?
The problem is that any review will need to look at facts, something that those opposed to HS2 tend to struggle with.
Facts like the number of passengers between London and the West Midlands, North West and Scotland have seen a 70% increase between 2009 (when HS2 was announced) and 2018 (latest data available). This compares with the expected 25% growth over the same time period, and the 52% growth until the opening of Phase 1 or the 56% growth until the opening of Phase 2a.
Now percentages are a bit ambiguous, so we can look at actual numbers. Given the fact that there's limited scope to travel between London and the North West (unlike the West Midlands and Scotland) we'll use those figures:
2009 (actual) - 6,576,000
2026 (predicted) - 10,006,000 - phase 1 opening
2027 (predicted) - 10,256,000 - phase 2a opening
2018 (actual) - 11,213,000
That's about 1,000,000 (1 million) more trips between London and the North West than were predicted to be happening at the opening of Phase 2a. That's before you take into account the 3.1% growth which Virgin Trains saw in the last year (which may be higher/lower on the London/North West flows, but is likely to be more growth).
With information like that it's going to be hard to justify canceling HS2 without a viable alternative. Even if there's extra costs (much of which is likely to be just allowances for inflation) it's likely that the extra passengers would fund much of the gap. Especially given that those extra passengers effectively wouldn't need to cover the running costs of the trains.
It (rail growth) is why I think that any experiment with only reserved seats on trains is likely to be short lived (even if that's 10 years) as, even with HS2, demand is likely to overtake supply fairly quickly.