But the question then remains, since power needs to be run to each module, why not communication bus wires too?
There is no compelling argument against a hardwired LAN. For many years, I was strongly in the "use wires whenever possible" camp. But, confronting the practical realities of my upcoming build, combined with real-world experience with ESPHome has caused me to reevaluate. I am actually kind of surprised that my position has changed on something that I once thought was totally obvious, but it has. If I were designing some closed system that I believed would rarely change (e.g, an HVAC system in a large building) I would still tend to prefer wire. But, all of my vans have proven to be open-ended experiments, and that tips the balance for me.
This is not an issue that I feel like proselytizing about -- there are arguments both ways. But here are what I see as the arguments for wireless:
--WIreless technology, and WiFi in particular, has become VERY robust, due to its wide deployment in the consumer world. The likelihood of serious performance or reliability issues in machine-to-machine applications has gotten very low.
--Wireless is likely to be more robust, not less, in a mobile environment, since there is nothing physical to break (to speak of). And, most problems can be debugged without often-difficult physical access. Of course, wired LANs can be made arbitrarily reliable, but doing so is neither easy nor inexpensive. I have no problem with folks who enjoy this challenge, but do not underestimate it.
--Comparing LAN wiring with power wiring is fair, but the fairness depends on the choice of LAN topology. Most wired LANs use star topologies for bandwidth and maintainability reasons. Such topologies are a lot more complex than a simple electrical bus. The historical exceptions, such as RS-485, have many limitations and tend to be difficult to scale. This, of course, leads to CANbus. There are very good reasons why the automotive industry has gone this route. It is a true distributed daisy-chain network and is indeed on the same order of complexity as power wiring. If you are prepared for all of the complexity of going to a CANbus-based system, then I have no quibble with it. Be prepared for a science experiment, though. And make sure that the wiring is very robust, since every inch of it is a potential point of failure.
--Extensibility: This is probably the thing that tipped the balance for me. With a wireless lan, slapping in a new node is a casual project, anywhere power is available. For example, deciding to put a new light switch somewhere you overlooked is trivial. Putting a temperature sensor on your under-chassis tanks--no problem. If your style is to design/build/walk-away, this doesn't apply. But, that is not my style at all.
--Maintainability: The thing that won me over to ESPhome in particular was the seamless way they handle OTA updates. Once ESP is running on a node, you never have to plug it into a computer again. Remote updating is like falling off a log. You can add features from the comfort of your living room. Yes, this could in principle be done with CANbus etc, but actually doing it with hobbyist MPUs would be quite a project as far as I can see.
--Hardware simplicity: The existence of SOC processors with on-chip WiFi an Bluetooth (such as the ESP32) means that simple nodes can be almost unbelievably simple from a hardware perspective. And simple means reliable. Again, not a show-stopper, but I have found working with such MPUs to be incredibly pleasant and productive,
Again, I am not really trying to convince anybody here--I will leave it to someone else to develop the list of advantages of wired LANs. But I did want to lay out the arguments that led to my conversion on this point.