If a person has never heard of dot stuffing they're never going to believe what other horrors lie within the email space. Header folding, quoting in the local part, ipv6 literals, etc.
Everything that is normally annoying with IPv6 literals, plus the fact that it's encapsulated as [IPV6:<the address>] and the address could take a dumb form such as ::1.2.3.4. But I mentioned it because it might initially seem to a neophyte in this field that the thing to the right of the rightmost @ sign is a name you can pass to your resolver. It might not be.
Note that IPv4 address literals are encoded in square brackets (e.g., user@[127.0.0.1]), so it's really all IP address literals that could be a problem rather than specifically IPv6 literals.