Here are some ideas for functionality. The session host could be responsible for assigning/removing crew users for trains incase there are players who would like to operate solo. Or perhaps it could be a first come first serve basis with the first person who claims a train as the engineer(as it is now) and the second user as the conducter who asked to engineer to be a park of his/her crew. The first user (engineer) would then have to power at anytime to remove/add to his crew.
Concerns that have been brough up so far:
"This would be boring for the guard (Conductor).."
This is aimed toward trainz users who would like to play more Prototypically. Trains do not operate without at least a Conductor and an engineer with the engineer running the controls while the Conductor reminds him of speed restrictions, work zones, communicates with dispatch and remains vigilant for visible defects. This could sounds boring for most trainz users but again this is something that a user could do only if they choose as a user would only be assigned as the second user of a train if he asked to be. Otherwise players will allways have the option to operate solo just like how we do now.
"It could be confusing if two users are trying to control the same locomotive..."
Players of the same train should communicate over chat or some other communication service like teamspeak. roles and expectations should be clearly communicated by the user who selected the train first. If the second user does not want to comply the second user should select and run their own train.
"What if users fight over control of a train?"
First come first serve. The user who first selects a train will have the power to remove or add user to his/her train
"Could the server's handle more users on one train"
To my knowledge there is a cap to how many users can play on a single server. The cap would still be observed only instead of 20 or so user moving 20 trains arround a map there could be 20 or so users moving 10 trains arround a map which, correct me if im wrong, is better for the server anyway as less train movement needs to be accounted for.
Please feel free to ask questions, voice concerns amd give suggestions. Im am trying my utmost to get some traction on this.