The key point is that all v6 addresses are owned by v4 addresses and therefore tunnelable, and that tunneling support is mandatory. There is no external prereq to having an individual device be able to open connections to v6 addresses, and only support at the router (with a public address) is needed to receive connections from any v6 address.

There is no way around upgrading end devices. But the problem with v6 adoption isn't the number of end devices from before 1995.

Basically the adoption plan could have been:

1. Get end OSs to have v6 support. They gain the ability to make outgoing connections to v6 addresses right away. There's no reason, from the beginning, for this not to be enabled by default with zero configuration from the beginning.

2. Get NAT routers at the edge to have v6 support. Gains the ability to publish services from inside without awkward port forwarding etc (and increases the benefit of 1)

3. Slowly make v4 addresses expensive so that consumers make do with less than a /32. They need v6 capable endpoints but can communicate as clients with anyone, and as servers with anyone who has adopted v6

4. Eventually v4 addresses are so expensive, and the number of machines running browsers that don't support v6 so small, that small time web sites stop taking a /32

etc. it doesn't really matter when the network backbones upgrade, it just saves a few bytes on the wire and they internalize the cost of that

This just doesn't seem like what happened in our timeline.