As much as this would be handy for people, I really can't see this passing the cost benefit ratio. The B&T is easy because the line already exists so it's mostly just some new stations and new signalling. It'll cost a fortune to build a whole new railway line which mostly passes through nowhere really (no large settlement >100k). Stuff like the Metro through the West End or the Tees Valley Metro will get built before fantasy ideas like this (and that's never happening neither).