Carlisle is not a "major" anything. It's a relatively small city of relatively low modern-day economic significance (much as it's a nice place and provided I could secure employment I really wouldn't mind to live there). The majority of demand from Leeds towards Carlisle is going to be onwards to Scotland, not *to* Carlisle, and it can just as easily go via the ECML instead. The tourists really are the biggest potential market for the line - you could argue that they would do better with a "Glacier Express" style service than an InterCity type train if you were going to do that. (Like the West Highland Lines, it's a line I think isn't used to its tourist potential - dedicated trains with proper panoramic First Class would be money for old rope - you might almost get away with doing something like that using 68-hauled Mk3s due to the very large windows).