My latest suggestion is as follows. The Thameslink route between Sutton (Surrey) and St Albans (Hertfordshire).This would allow the use of the current changeover at Farringdon as well as services going both ways around the Sutton loop via Wimbledon or Mitcham Junction. Any period from 1987- Present could be chosen with motive power from classes 319, 377, 387 and the current 700.
Looking at it on maps I’m thinking maybe DTG could try do Luton to Croydon (if thameslink run from Luton) but St Albans to Sutton sounds really good. Edit: you could also have a the link with east Croydon from Tulse hill so you could have the St Albins- Sutton/East Croydon Edit 2: if DTG really stretch it and want their money’s worth Luton town/Luton airport parkway-Gatwick airport. That would be really unlikely but I want to see them try with that one.
Sounds good, it's a decent length but nothing unreasonable like some other Thameslink suggestions. It also includes a whole Service so we will be able to drive trains without them buggering off into a portal.