Try an IPv6-only VPS and see how quickly something breaks for you. Dual-stack fails miserably when the newer stack is incompatible with the older one. With a stack that extends the old stack, you always have something to fallback to.

To replace something, you embrace it and extend it so the old version can be effectively phrased out.

> Try an IPv6-only VPS and see how quickly something breaks for you.

Who's arguing for that? That would be completely non-viable even today, and even with NAT64 it would be annoying.

> Dual-stack fails miserably when the newer stack is incompatible with the older one.

Does it? All my clients and servers are dual stack.

> With a stack that extends the old stack, you always have something to fallback to.

Yes, v4/v6 dual stack is indeed great!

> To replace something, you embrace it and extend it so the old version can be effectively phrased out.

Some changes unfortunately really are breaking. Sometimes you can do a flag day, sometimes you drag out the migration over years or decades, sometimes you get something in between.

We'll probably be done in a few more decades, hopefully sooner. I don't see how else it could have realistically worked, other than maybe through top-down decree, which might just have wasted more resources than the transition we ended up with.