Congratulations from the Simutrans Team for the Steam Release!
Simutrans launched on Steam five years ago when HaydenRead (the very original poster of this thread) also offered himself for this - I've always thought that it was weird that our greater cousin didn't do the same!
HaydenRead left some time ago, leaving the game unmaintained (you better somewhat prevent this) until some months ago, when I picked up the maintainership. So I know for sure what a gargantuan task is it
I have learned a thing or two about deploying to Steam in the process - so I may be of some help, if you need it, I will gladly offer it.
I also consider a good decision not to support the Workshop - even if the players demand it, it is far better a build-in mod manager, and other great games like Factorio also take this approach.
P.D.: About the linux support, I would argue that it is not realistic to support anything older than Ubuntu 18.04 (maybe 16.04 if you feel generous). I looked at Steam Statistics for Simutrans when I started messing with it and there was
absolutely no one playing on versions older than Ubuntu 18.04. Take in mind that Steam population (aka gamers) don't usually play on outdated systems for obvious reasons (a lot of my players are playign on rolling release distros indeed). And those on machine with older specs will try to avoid Steam if possible.