and they're not needed on IPv6, just the same as we don't require cars to have horseshoes, even though horses needed them before.
Anyway, I'm on HN right now over NAT because HN doesn't have a IPv6 endpoint, otherwise I would be here over IPv6. THAT is what is holding IPv6 back, there aren't the services on IPv6 so there is no user demand for it.
But that may not represent the full story for them. Internal moderation and anti-spam may need updating to be compatible with running on two different networks that each have different approaches to numbering.
Even companies that 'get' v6 sometimes have rough edges. E.g. Cloudflare - which has been a great supporter of v6 for a long time now - has been known to send 'log in from a new IP address!' notifications because my machine automatically rotated it's IPv6 privacy suffix.
Either you get that message or the IPv6 privacy mechanism is not working well enough.