What happens when there are literally truly no IPv4 addresses left for sale? Not today’s reality, but the clock is ticking.

There will always be IPv4 for sale just as there is always land for sale.

This is the “oil will never run out” argument. Technically true, but irrelevant.

I chose my analogy carefully. Oil is consumed but land and IP addresses are not.

You can't really just "find" more IPv4 though. Cloud platforms are eating blocks for breakfast, lunch and dinner, and while it's always going to be for sale, there's no reason to expect you'll be able to afford it.

Fortunately, if you can't afford IPv4 then no one else can afford it either, which means the incentive to adopt IPv6 is extremely strong and thus you no longer need IPv4.

Existing large ISPs and cloud providers with remaining IPv4 addresses and no IPv6 support are not going to have a strong incentive until after the damage is already done.

Why won’t Google, Cloudflare, AWS, etc. simply own all most IPv4 addresses and leave all end users using NAT (or even CGNAT) to access them? This cements their businesses, since then nobody can reasonably host their own servers except through them.

It works both ways though, doesn't it? If you are IPv4 only, you can't access/can't be accessed from the whole internet. If you are IPv6 only, same applies.

No, because there is nothing interesting that's IPv6-only.

That depends a great deal on what country / language is your norm.

Which country/language has interesting IPv6-only content?