Option 5: ffff/96 (yes I get it, only works if host has both ipv4 and ipv6, on the plus side: no need for the network to support it. Mostly for applications)
The issue is most of these require ISPs to deploy new hardware, or deploy new network services. The problem is that network hardware is single-purpose, because only single purpose hardware can sustain the speeds we demand of internet networks. This means a lot of hardware needs to be replaced in order to make the global IPv6 transition and, short of redesigning IPv4, which is 43 years old now, there's no other way to make the transition. All these solutions require either work by your ISP, or work by you yourself on all your hosts.
NAT64+DNS64 is the best transition method as it eliminates the need for dual-stack.
Clients can be IPv6 only and ideally need a CLAT installed to handle the edge case of IPv4 literals in apps that don't use DNS. The ISP's internal network can be IPv6 only. Only this NAT64 translator needs to speak both IPv6 and IPv4, and only for non-IPv6 traffic.
On hacker news. You're going to find a big contingent of people who are getting things like VPS/colo/dedicated/cloud hosting, only get an IPv6 address on that (or finding that an IPv4 address costs extra) ... and are occasionally finding some customers can't reach their sites without every host having an IPv4 address or paying for something like cloudflare.
So there is a bit of a demand, especially here, for forward compatibility.
Option 1: "6to4" https://en.wikipedia.org/wiki/6to4
Option 2: "nat64" https://en.wikipedia.org/wiki/NAT64 + DNS64
Option 2b: "nat46" (which makes a few ipv6 hosts available over ipv4 if yo ulike)
Option 3: "Teredo" (also known as "6in4" "tunnel broker" "6over4" "tunneling" ...) https://en.wikipedia.org/wiki/Teredo_tunneling
Option 4: 6rd https://en.wikipedia.org/wiki/IPv6_rapid_deployment
Option 5: ffff/96 (yes I get it, only works if host has both ipv4 and ipv6, on the plus side: no need for the network to support it. Mostly for applications)
Option 6: DS-lite https://en.wikipedia.org/wiki/IPv6_transition_mechanism#Dual...
And then there's the weird ones: https://en.wikipedia.org/wiki/IPv6_transition_mechanism
The issue is most of these require ISPs to deploy new hardware, or deploy new network services. The problem is that network hardware is single-purpose, because only single purpose hardware can sustain the speeds we demand of internet networks. This means a lot of hardware needs to be replaced in order to make the global IPv6 transition and, short of redesigning IPv4, which is 43 years old now, there's no other way to make the transition. All these solutions require either work by your ISP, or work by you yourself on all your hosts.