"I don't know about other link systems, but sega seems to love fibre optical ring buffers. (S32, M1, M2 etc.)"
Namco used something along the same lines for Suzuka 8 Hours 2(and presumably other similar hardware games), except instead of fiber cables they used standard 75ohm RCA/video cables. The 5th display on that setup just had an extra output going to the tower where it had a full extra System2 PCB setup to just run that. It received input only, had no network feedback to the rest of the system. Only difference on the PCB was one of the DIP switch settings to change it to tower mode. I had to fix up one of these at the arcade I used to work at.
We had a Virtua Racing quad setup, but after years of abuse and a previous tech that had no clue, I was only able to "rescue" a single twin unit from the whole thing. All 5 monitors were in various states of non-working. 4 of the boardsets had problems, and I had to mix and match CPU/video boards to make 2 working sets. It was beyond our budget to fix the whole setup, plus the previous tech had also thrown away(!?) the live race monitor cabinet portion, so I never got to see that in action.
I did ship the dead boards to Guru, and I think he dumped the surface mount TGP ROM's from those so they weren't totally wasted.