After a fair bit of reflection, this is what I think the end-state of HS2 will be as of 2050-2055:
It seems likely Labour's review will conclude that at a minimum HS2 2a is necessary, although I suspect that will be the last project associated with "HS2" as a brand. It is a brand which has unfortunately become toxic at this point.
The next bit of infrastructure we'll likely see will be a solution to the Castlefield issue (This likely in the form of a simple point-point bypass tunnel), followed by a new line to Liverpool roughly following the M60, making it fairly simple and cheap to construct compared to the route via the airport that added significantly to the cost of NPR, so much so the economics don't stack up without HS2 following it also.
The last piece in the jigsaw will likely be essentially the same route from Crewe as far as Tatton, only connecting with the east-west NPR line near Cadishead (instead of running via Mcr Airport)
I'd also hazard as guess trains will be limited to a more standard 260m in length, which should make constructing an underground through station in manchester for example, much cheaper. The side effect of this however is we';; need ore trains to compensate. Swings and roundabouts much?
In terms of links to Leeds, I can't see anything more than TRU being delivered pre-2055, mostly due to just how expensive such a line would be. Using known nodes and the rough TfN alignment, I've found roughly 50% of the line would be in tunnel. If it were built, I'd suspect two stages: Mcr to east of Marsden, and north of Huddersfield to Leeds.
In terms of Golborne link to Scotland, in my view, get it built! Only there just doesn't seem political appetite for it, and with a purpose-built link into Liverpool, and more trains using the line from those cities (shorter train sets) it should use up HS2's capacity, thereby not hitting the BCR so hard by missing the link.
Marshy.