I imagine a product manager took exactly 100ms to calculate that the answer to that question is "functionally no one" and so there went the $X ethernet connector from the build, for patently obvious reasons.
Hell, I'd love to know Sonos's ethernet adoption rate, since they certainly have that data. I'd bet it's fairly high since Sonos is a bit up-market and sometimes professionally installed, or installed by enthusiasts, but I'm willing to guess it's < 5%, and realistically, < 1%, even if we only obviously limit the sample size to "Sonos devices that are eth capable."
I generally like receiving a notification when the dishwasher is finished with the dishes, but with the current WiFi setup it's always broken and I don't have the energy to fix it. So I would've used it if it were working over Ethernet and I'm not using it now when it can only work over WiFi.
Out of home automation devices Philips Hue works only over Ethernet, though there you have the advantage that you can place the hub anywhere you like.