If we are talking about a journey on an end to end basis, then as far as Lumo examples go you have to look at the air demand figures as a base to start with.
Over 3 million passengers were handled pre covid from Edinburgh Airport to the big five airports in London, with strikingly similar city-centre to city-centre journey times (~4 hours).
I'm not sure anywhere else in the UK could match this.
Maybe Glasgow (which handled around 2 million London passengers pre covid), but there'd be issues posed when you boil down into the details of trying to replicate Lumo's model on the WCML due to various factors including available paths, demand, journey times (re tilt), and where the ORR stand on it based on their criteria for Open Access on revenue extraction and BCR.