That's true when we are talking about /48s. There are enough /48s to hand out to everyone (and then everyone gets 65K networks to work with). In the current Global Unicast space (prefixes starting with 001) there are 2^45 /48s. Effectively unlimited number, as there are 2^33 people on earth - so everyone would get 2^12 /48s.

There are 2^21 /24s in the existing Global Unicast Space. About 2 million. A large number, to be sure. But if every entity in the world MITs size asked for a /24, we'd start burning through them pretty quickly....

Isn't that what they once said about IPv4 when they were divvying it up?

Orders of Magnitude are completely different, of course. When MIT got it's /8, (one of just 255 available), it gave them the ability to create 2^16 networks with just 254 hosts on each one.

Now, anyone who wants to can ask for a /48, and they are automatically given it, and they are able to create 2^16 networks, each network with an effectively infinite number of hosts on it. And, there are so many /48s on the (current) Global Unicast space (prefixes starting with 001), that everyone on earth could be granted 4000 of them. And, in reality, ISPs started already conserving, and handing out /56s instead of /48s to most consumers/SoHo - further increasing that number by 255x.

And that's just the 001 prefix. Based on what we learn about allocating space there, new policies can be device for the other 6 prefixes available. We aren't going to run out of IPv6 address space.