If your site depends on a DNS extension that's only 3.5 years old (and designed to be optional), I think it's fair to say your site is just offline for some users due to a config mistake.
You're free to set up your servers however you like, but there's wisdom in Postel's law.
For the lazy like me: robustness principle, aka Postel's law
https://en.wikipedia.org/wiki/Robustness_principle
Thank you for the reference. I learned something today!
> A flaw can become entrenched as a de facto standard. Any implementation of the protocol is required to replicate the aberrant behavior, or it is not interoperable. This is both a consequence of applying Postel's advice, and a product of a natural reluctance to avoid fatal error conditions.
[0] https://tools.ietf.org/html/draft-iab-protocol-maintenance-0...