I think cool addition to TSW 2 would be the Heathrow express branch. It would use the Heathrow express class 387 with also potentially the TFL rail class 345 from London Paddington to Heathrow T5 and would add the underground station as you go on the overpass just past Hayes and Harlington. With the GWR already in TSW 2 and even the overpass that leads into the underground tunnels there's a lot less to implement into the route to make it possible.
Heathrow Express hasn’t accepted a licence from DTG and GWE is set in 2016 before there were Class 345’s and Class 387’s.
