- IPv6 Peerage.
- An IPv4 or IPv6 broker.
- First party software configuration.
- Support from upstream and downstream from infrastructure/partners and configuration.
It is a significant project. People think you just assign an IPv6 IP, throw in a AAAA record, and then it magically just works. More than likely you'd just create a block-hole where IPv6 traffic goes to die.
It's still called a black hole.
Address classification changes are real work. I haven't done heavy benchmarks, but bigger addresses and everything else probably does add up to a measurable server performance drop, but that's balanced by real world networking performance improvements for users with nasty network stuff on IPv4 and less for IPv6. Otoh, I'd guess HN isn't bottlenecked by networking anyway.
If you aren't hosting the infrastructure yourself then you are limited in what you can support but you wouldn't be worried about peering, brokers, or up/downstream providers since thats what you would be paying the hosting provider for.
But something like HN probably has various moderation/spam preventing tools that assume IPV4.
I believe people have made IPv6 gateways to the ipv4 content.