Who travels from Carlisle to Stirling?
Both are on routes to more important destinations - if this is for connectivity south, far better to try reach Preston at least - especially if that age-old 'Scots to Blackpool' stuff still rings true. On the other side, Inverness or Aberdeen (or at minimum Perth/Dundee) might attract more usage.
But perhaps this is for Motherwell, Cumbernauld and the general Central Belt to avoid heading into either city to head south, in which case, perhaps getting to Manchester or Birmingham is best. London has of course, more demand than both combined - but a longer slog.
I can't help feeling that this might work better if Grand Union
have to go to London:
Dundee > (Dundee West/Ninewells >) Perth > Stirling > Larbert (for Falkirk) > Cumbernauld > Whifflet > Motherwell > Lockerbie > Carlisle > Preston > Crewe > Nuneaton > Milton Keynes Central > London Euston
alternating Whifflet and Lockerbie.
There's probably some Dundee > WCML demand, even if not much; and the West Midlands are a change away at Crewe. It seems very daft to run it only as far as Stirling if you're going to do it at all. Motherwell and Lockerbie might also pick up some Edinburgh/Glasgow traffic if the tickets are cheap enough; in fact, that's probably the main survival hope of the service – to undercut Avanti from Glasgow. If the ORR OK'd the original proposal, but – like GNWR to Blackpool – vetoed the Crewe stop, I think it'd be difficult for it to survive unless Carlisle > Birmingham via Nuneaton, or Glasgow/Edinburgh > Birmingham via Lockerbie and Nuneaton, was competitive with Virgin's direct service.
I still think (unsurprisingly considering why I resurrected the thread) that Cumbernauld makes more sense than Greenfaulds as a stop, despite the latter having marginally better Park & Ride potential for Kilsyth, Moodiesburn and Chryston. Similarly I'm not entirely convinced by Whifflet rather than Coatbridge Central, but I'll let that slide considering that Whifflet has better connectivity to the likes of Rutherglen and Kirkwood.
Aberdeen is a decent aspiration for the route. I think Inverness would be too, but that's a long-term ambition because there's no point in taking a path away from the Highland Mainline that doesn't serve Glasgow
or Edinburgh directly. Indeed, that's one of the reasons why an extension to Perth (and Dundee) makes sense; if timed to connect with ScotRail services from Inverness to Edinburgh via Fife (which is hard because there'll also be a connecting service to Glasgow via Stirling and Lenzie in that instance), then you get a quicker Inverness to London journey time. After all, the Highland Chieftain always seems to do well in terms of end-to-end (or England-to-Inverness) traffic.
An Aberdeen extension might be easier to path – there's still Usan to contend with – you'll have to forgive my ignorance here as I expect that the ECML north of Dundee is already fit to bursting, but I don't know entirely. I do know, however, that there's already Aberdeen Crossrail to factor in at the northern end. If the whole thing isn't too difficult to do, then some differentiation might be needed – maybe go Dundee - Carnoustie - Arbroath - Stonehaven - Aberdeen? – but it's possible that a Dundee extension might suffice.
Suspect that Stirling as the Northern location is more to do with the lack of wires beyond and that the aspiration would be to extend as the OLE roles out North.
Never mind. Although, if this proposal
does ever get off the ground, then there'll probably be wires up to Thurso, Wick and Mallaig by the time the first train runs...