It's been stated numerous times by dtg that an editor will never come to tsw due to various reasons I do not remember. Same with multiplayer cuz dtg only want to focus on the single player experience and getting it right.
That was Sam during a livestream basically saying: "if it's not on the roadmap, it's not being worked on". There's still a possibility in my opinion.
Yeah no from DTG but there is still Unofficial editor work in progress... there one day you should be able to build the whole route and add your own locos, wagons, safety system, etc...
Long, long ago, Matt explained very convincingly why DTG is not likely to ever introduce a full-fledged editor (route & scenario) for TSW. I've tried searching for this information, but, as so often happens, haven't had any luck.
