Yeah I had a quick conversation with Rolly he has seen serial versions, but it depends on if it's a modernization job. Without a serial interface though, the hall buttons almost certainly be hard wired inputs which is what's shown. The 8400 (series 1) buttons were used with the E401, 31VDC. The series 1 were used with LRV-3 and LRV-4 but they use tone communications not serial. I'm fairly certain the two pieces you would need for serial is a serial interface group board and the group remote serial comm stations. Not sure if the group fixture I/o board can do serial inputs or if you have to wire into the group dispatcher board for serial hall calls.
All Otis stuff to my knowledge now has gone to 4 wire serial with 2 30VDC power and a communication twisted pair. Old elevators had tons of wires
