I don't know about other models, but some Lagunas certainly do have some multiplex wiring. Versions with memory mirrors and seats have these functions controlled via multiplex, though on other models they're conventionally wired.
The question on the towbar thread was whether or not the road lights are multiplexed. The indications I've seen so far would suggest that they're not. Specifically:
1) Renault's towbar wiring loom does not use bypass relays (though the lights might still be multiplexed, and maybe Renault believe the multiplex controllers can handle the extra load and potential faults.)
2) The point of multiplex wiring is to reduce the complexity of looms by sending just a power and a 'data' line to various computer modules around the car rather than powering each component individually. If this were the case on the Laguna, then I wouldn't expect to hear the relay for the rear fog lights activate behind the dash when I switch them on or off.
3) The various bits of wiring that I've seen suggest that looms with numerous wires are still present throughout the car. Though they could still be controlled by multiplex controllers, that would kind of defeat the whole object. I wouldn't expect to see much in the way of wiring on a multiplex system - just power lines and a common 'data' line to the various controllers, and then short runs of wiring from them to the controlled components.
I honestly don't think we're ever going to get a definitive answer on this one. I've asked the question in the past, and none of the resident Renault techs were ever prepared to bite. Somebody somewhere must know for sure, but they're keeping the information to themselves
Of course the real question on the towbar thread was whether or not bypass relays are necessary. Renault themselves clearly think they're not. If that's their view, then who am I to argue?