Go Transit is the most popular system in the world. They have the best routes and literally best of everything. All the routes which are added, are just reskins and are pretty boring. Go transit offers so much and there expanding in the coming years. Multiplayer would be very nice for real operations for freight and passenger. Would be so fun, and the player count would be so high.
AFAIR GO have refused approaches from DTG for a licence. Multiplayer has been discussed to death but TBH is catered for by Run 8 and SimRail. There’s really nothing TSW does that would be enhanced by MP.
