It's an interesting idea, though when you consider that a lot of the people who use public transport in London don't actually live in London, and some services

It's an interesting idea, though when you consider that a lot of the people who use public transport in London don't actually live in London, and some services extend outside of London, it does raise a lot of questions. And that's before you even get into the political factors. Those challenges aren't necessarily insurmountable, but I imagine it would be a lot more complicated to do than it might first appear.