Rail signal conditions

[anmoch]

Could we get a way to set conditions on rail signals to control what trains can pass through them?

For example, by setting "train wagon = 0" on entry signals into track sections, you can make sections that can only be used by player trains that only consist of locomotives. This would allow building high-speed sections for players.

If the signals included both the train itself (locomotives+wagons) and its contents, other possibilities arise, such as forcing copper/iron trains to separate holding areas without having to then have separate paths between holding area and unloading, etc.