Certainly not Northern's inferior service of rotting 40 year old 2 car DMUs.
By 2050 or whenever phase 2 gets back on the table, I'd imagine Northern rail routes to be in a much better state than now, if things like the Bee/Weaver/Merseyrail networks and light rail expansion continue.
May be an idealist viewpoint but I'd rather have a rail network designed optimally for the public transport user, focus being on those who walk, cycle or take the bus or tram. If you achieve such a thing, those who still want to drive the whole way after that are likely to not be attracted by any carrots or sticks.
The Benelux (primarily ne and lux) has a fairly optimal national transport network - despite that, many people still don't take public transport. However, it's a much smaller proportion than in the UK, to the point that the total carbon footprint of these drivers is really low (and getting lower as EV usage increases) and it really isn't negatively affecting places through 'car is king'-minded development because it's a minority.
If there were the capacity (which there wouldn't be if the full HS2 plan were to come to fruition) to add stops between OOC and Birmingham Interchange, a stop somewhere near Claydon/Winslow still makes more sense than an M25 Parkway. You'd get the same amount of benefits but significantly less road congestion by improving rail links between the Chilterns and Birmingham, such as through a CML 4-tracking and electrification project or the EWR Aylesbury spur. Moor Street station will be a few paces from Curzon Street, it'll be a very easy transfer. Plus, the Chiltern-OOC link will be a really straightforward travel option and the speed of HS2 offsets the double-back.
Those who will always pick sitting in traffic on the motorway over changing once or twice along a train journey will never be won over so it's no use pandering to these people by building an M25 Parkway in the same way as it's no use pandering to the Chiltern NIMBYs. Stockport and Manchester Airport HS2 have/would have many more roles than just a parkway. One's a dense urban centre, the other serves the main non-London airport.
But HS2 will have a LOT of extra capacity...
Given that probably the number one complaint about UK railways is high ticket prices, you could easily fill those seats by making the fares affordable, no need for an M25 Parkway. Would be really politically popular too and may revive some public favour in High Speed Rail which is desperately needed.
In the event that you have a high-speed line that has both ample spare capacity and cheap fares, then you can start thinking about where else to bring passengers from (e.g. along the M25 corridor, or Buckinghamshire). For that there needs to be more than one North-South HSR in the UK though.
And the impression I get is SNCF wish they did not stop at intermediate stations.
That's largely because most of those stations were designed very poorly, with no integration with regional rail or buses. So instead of these stops being quite a useful transport hub for the surrounding region, it's a cut-off parkway stop. If there were better connectivity and regular calls at these stations, they'd be well-used and would likely win a few rural votes. SNCF isn't too interested in building an integrated network though, their focus is on profitable intercity services. If you live outside a 50k+ city, they'd prefer if you drove the whole way. With that in mind, you can see why they see these stops as a waste of money, but that's only because they designed it that way.
The French also had capacity in their existing terminals following the construction of the RER system so didn't need to build the new routes right into the heart of the cities served.
This is an important consideration. HS2 (and any other subsequent HSLs) would be much easier and cheaper if London had 2 or 3 crossrails instead of just one, but currently many commuter lines still run into the mainline termini.
