Haven't they been telling people to do that since before it became reserved? If so, the problem is more that you can't "reserve" something that's already in wide use, and mdns should've used something like .mdns.

It's like when .dev became a gTLD, knowingly breaking a bunch of setups for a mix of vanity and a cash grab. Obviously dropped the ball on the engineering side.

Seems more a reason to never use stuff you don't actually control and are reserved for future purposes. Everyone knew who was in charge of DNS TLDs and that while they were being at first conservative in how many they assigned, they reserved the right to assign as many as they wanted.

But also, yes Microsoft documentation used .local before mDNS reserved it, and IIRC Microsoft was also involved in suggesting it for mDNS as mDNS came out of the multi-company standardization efforts from Apple's Bonjour. That said, my impression of most of that documentation from that time is that it was incorrectly using .local as a fake TLD where they should have been using .example or .example.com and also pointing people to the RFCs that those were not valid choices in a real setup. A problem with such documentation is that it is too easy to take literally. A follow up problem was sort of the "accidental security through obscurity" benefits of using non-globally resolvable addresses becomes "best practice" through essentially stubbornness and status quo (related to all the recent rediscussions on HN about NAT44 is not a firewall except by accident and you can have very good firewalls that aren't NAT44).