I dont care what loco but we need steam the game has been out for far too long to not have steam yet, you can't truly call it a train simulator if there isn't any steam.
I would love a steam-era route (like the Pennsylvania RR, NYC, or UP Sherman Hill in the 1940s-50s). I really don't know how steam locos would be done in the game. I agree that they would be amazing with all the motion and sound. Maybe DTG could start small with a heritage route (like Ffestiniog or something like that) and move up to the bigger engines we all want (Big Boy, maybe). An automatic fireman feature has been used in previous train sim games and could work in TSW2020. Multiplayer would make running a steam loco interesting, too.
I would love steam trains to be added but I would not expect anything any time soon. If DTG were to release steam trains in the future I would assume the first route to get any sort of steam locomotive would be the West Somerset Railway (WSR is a heritage route) and I would not expect any massive steam locomotive. I think if DTG were going to add steam trains in the future they should start with a pannier tank. The above image is a pannier tank on the West Somerset Railway. In my opinion, f I was DTG and I was going to add steam locomotives in the future I would start with a pannier tank and I would make it for the West Somerset Railway route as a Loco DLC.
I'd like something like an LNER Peppercorn A1, or A3. Indeed on the opposite coast, LMS Coronation class, or Princess Royal. Even something earlier would be welcome, GWR 3700 class (including 'City of Truro') would be welcome (pre 'Big-Four"). Finally, some Pullman coaches would be nice, whether that's on WSR, or on a new route set pre-nationalisation. I'm now rambling, but talking about Pullman, it would be extremley difficult as there are none surviving, and few recordings of its sound, but the Blue Pullman is something one could hope for, even if it will never come.
Matt has said in the past that steam trains are possible but they are not sure how difficult of an experience to make it. They’ve said that they aren’t currently working on steam so we will have to wait for the roadmap before we can get any info