Each rail (there are 2) is about 2 metres long, the ends are close together and from there, there is 2-3 metres of cable to the control cabinet. If needed, the powerline interface could be mounted close to the rails, but the preferred location would be in the cabinet.
Required datarate is 2400 - 9600 bps. One of the operations is a sync cycle that is currently handled by a separate hardwired signal to all modules. The response here is in the us range and this is obviously not possible through the powerline comms. I can compensate for a longer time as long as the delay is fixed. I might be able to relief the jitter requirement by changing/elaborating the sync cycle if needed.
Most other commands require a response within 10 - 100ms. All commands are only a few bytes long (2 - 5).