First time I've encounterd this line was in TS2024 Classic which was a route mixed up with a narrow gauge line where a little steamer ran on it and a personell carrier did some small jobs. Then you had the main line where a old UK stock ran on itm the BR483. There are a few steamers in TSW in functional state and I think that's good enough for me to get the old narrow gauge line opened up again with the little steamer there and passanger operations again along with first of it's kind the personell carrier. I would tottaly be cool with it. The steamer was called 04 OST Invincible, it had a very stunning high pitch whistle and it usually ran about 2 carriges. You could possibly add the RED vintage unit from London underground as well on it. On the mainline also the BR 2EPB made it's apperance as well in TS 2024.
Just a small correction, the IOW Steam Railway is actually standard not narrow gauge… I always thought a replica of the original steam network on the IOW would be fun and a self contained little world you could lose yourself in. Sadly it would need a policy rethink on steam traction and historical routes by DTG.
