Well since DTG’s focus is on high speed then I’d assume we still do have a chance to see them get added to TSW.
Just saw the new update on TSW2 roadmap with GWE added. Before we get any class 387 or class 800, we can repaint the class 377 and class 395 into GWR and run it on GWE!
A few years later, we have the class 387 coming with the brighton mainline, hopefully this means it gets added to the GWR, all it would need is a new livery, and some wiring above the tracks.
No reason to annoy people with any replacements. At this point i want to use the opportunity to suggest the cl57 like in the picture.
For GWE in its current form, the best options for dlc are... Class 57 with Mk3 sleeper stock Class 165 dmu Class 180 dmu These were all in service around 2015 before the wires were completed. The Class 387 and 800 series would better suit a more recent version of any part of the GWML as we will almost certainly never get the current rendition of London Paddington to Reading. As far as a current rendition of GWR routes, it might be worth including the Class 769 (former 319) tri modes in areas surrounding Reading as they are pretty much in the fleet now.
That can fit this route and BML Reigate Branch to Gatwick Airport with class 166 also from GWML London Paddington to reading.
New Wiring isn't happening. GWE is set as the wires are going up, and will stay that way. Unless you're talking about a Heathrow Express 387 to Hayes & Harlington, it's practically off the cards.