The MAC address is not sent to the server, or accessible to web pages client-side, so that wouldn't matter.
I realize that the last time I liked at this was in the context of wireless devices on a private subnet - which is why I thought it might be relevant. However I am curious, why is it, then, that Windows 10 has gone for randomisation?
It is if you're using Chrome or got any Google related properties installed on your PC.
I don't think this happens. How do you think it's being transferred? A header sent only on requests to Google properties? A special JS API in Chrome that only Google knows to call?
In theory. But it's not impossible for a nefarious browser to send it along as an HTTP header. Or a nefarious AP:
Your link describes the Milan airport captive portal putting the MAC in the URL (don't do this). The referrer is automatically attached to any requests the page makes. This is a comically broken configuration, not something at all common.