to DTG i think it will be a good thing that you do crossrail in both games because it is a well known route and the signaling and train sytems
Much of the western end and the eastern end are already in game via the Western Mainline and GEML routes. The heathrow extension from Hayes and Harlington will never be in game unfortunately, as the route is wholly owned by the Heathrow Airport Company who don't do licensing. The core section and tunnels to Abbey Wood might be a thing in future but overall I think the route likely too long for TSW production
It would also necessitate the construction of the 345 as well. DTG have existing agreements with Bombardier and TfL so this could well be on the cards