Appreciating it is a RUK-bingo chestnut - linking Nottingham/Sheffield/Leeds to Glasgow does seem like a reasonable set of new city pairs to explore. There is no London, but these metros add up to significant populations without meaningful service to Western Scotland or Cumbria
Derby/ Sheffield/Leeds has a bi-hourly service to Glasgow with XC, pre Covid, presumably it’s official status is more like “going to get reinstated at some stage” rather than “been officially permanently scrapped”
As it was only a net cost of one unit (extending half of the Edinburgh services east of Waverley), it provided a lot more journey opportunities from the East Midlands/ Yorkshire to Clydeside than an equivalent “one unit” would provide over Ribblehead/ Beattock
But when it comes to long distance links, there are always going to be pairs of cities that we don’t have capacity to provide direct trains in between (the obvious two examples being the continual fascination on here with Brighton/ Liverpool etc, but see also Sunderland/ Hull/ Bradford/ Portsmouth…)
My other one on this, is another tired old chestnut - an iteration of Rio. St P pathing of course an issue - but London - Leicester/Derby to Stockport/Manchester - plus some competition for London-Manchester (acceptable for Birmingham/Chiltern, and in the interim, Avanti brand being in tatters too). And a service to the NW from either Bedford or a Luton in some hours.
Manchester must be Derby and Leicester's largest gaps
Nice in theory but…
1. There’s no capacity at the St Pancras for any more services (hence EMR having to order bespoke trains designed around the platform 240m lengths, rather than something like 802s that they could have in service already if they’d ordered “off the shelf”)
2. Given the number of Thameslink paths and the relative lack of demand for some intermediate journeys, all Leicester bound services run non stop to at least Kettering if not non-stop until Leicester - I don’t know if there’s going to be space to stop an OA service at Luton Airport/ Luton/ Bedford
3. If there is a lot of untapped demand for direct “Home Counties” to Manchester trains then why not stop more existing Manchester services at Watford etc? Maybe Bletchley too, once EW starts? Nuneaton and Tamworth for connections? Would be a lot easier than a whole separate service
4. In theory it’d provide competition from London to Manchester, but by the time you introduce such a service well soon be at the stage where Avanti becomes the cheaper/ slower alternative (to HS2) between the cities
5. The layout of lines/ stations in the East Midlands means that any “Manchester” service can only really service two of the “big three” (Leicester/ Nottingham/ Derby) - you seem to have decided that Leicester/ Derby need a Manchester service but Nottingham is there one in need of a Glasgow train - is that based on anything particular? Because if passengers from one of these cities would need to change to access your new service then that’s little difference to the (pre covid) timetable where Nottingham passengers could access Glasgow every couple of hours with one change at a Derby/ Sheffield and Leicester/ Derby passengers could access Manchester each hour with one change at Chesterfield/ Sheffield
6. Similarly, you mention “a service to the NW”, but terminating at Manchester leaves lots of places unserved (Liverpool, Blackpool etc), where do you draw the line in terms of trying to link pairs of places?
7. “Avoiding lines” seem to be a continual fascination on here (running from Huddersfield down the WCML avoiding Manchester by using the Denton line, avoiding Swansea by using the District Line, running straight from Bradford to the ECML by using the junction outside Leeds to avoid that station, there was a recent thread suggesting that we use the chord at Kensington Olympia to run services that run tantalisingly close to Central London without actually serving it). I get that It’d be faster for longer distance services (albeit you might be occupying the single track chord from Dronfield to Grindleford for chunks of each hour in each direction, a place that’s often used by a freight path that hasn’t got a MML timings that lined up perfectly with its Hope Valley path) but would the through passengers be more than using the resource for an East Midlands to Sheffield service and a Sheffield to Manchester service? Same goes with those who think the Milford Haven to a Cardiff passengers outweigh the Milford Haven to Swansea and Swansea to Cardiff trade etc.
I’m not totally against these two canards, there’s just about enough meat in the bones to warrant their regular discussion on here, the above is meant as constructive criticism rather than picking a fight, it’s just that I can’t see these two as a priority (even as a Scot living in Yorkshire who’d benefit from a cheaper “via Appleby” fare for journeys north of the border!)