Well GWR Route, in regards to the 387's the story is this. They replace the 166 so the devs would have to remove the 166 from the GWR DLC or create the same DLC again but instead the 166 have it replaced with the 387's if the whole thing would approve. We could accept the removal of 166 (give the players the option to install it again and everything that goes with it) to make it easier? How bad do we really want this unit that is the question as well because it poses some very complicated process https://www.railwaygazette.com/passenger/gwr-finalises-thames-valley-emu-order/42618.article
Why can’t we have both? 387s didn’t all turn up at once and all turbos scrapped within a day. Even to this day, 3.5 years after 387s were first introduced into service, turbos still operate out of London Paddington on a few diagrams. We shouldn’t have to delete turbos in order to have 387s. The same can be said about HSTs and Class 800s; although HSTs have gone for good on intercity services, there was a transitory period of roughly 18 months where they both worked together out of Paddington. Maybe if and when they do upgrade the GWR on TSW, they can set it in this transitory period so that all 4 traction are available. Regardless, turbos will always be there because they still operate out of Paddington. The reason why we haven’t got 387s yet on TSW is nothing to do with having to sacrifice turbos. It is because the developers need to put all the Overhead Line Equipment (OHLE) in as well as other signalling improvements/fixes. Otherwise, there is no reason why we couldn’t have 387s today as it is almost identical to the 377s.
It’s not at simple as you make it out to be. For one, the entire route would need to be changed and updated. A LOT of things have changed since 2016, which GWE is based in. Secondly, GWE itself won’t be updated. It is staying in the era of 2016, end of story. Finally, any update would be an entirely separate DLC. It would probably be easier to start again from scratch than to update GWE. GWE is staying as it is.
I think an extension to Manchester/Leeds or Brighton/Eastbourne are more likely to have extensions attached or maybe a Leeds to Darlington connection, but I can even remember Matt P saying GWR would not be added to and that was about 2 years ago.