"This is going to free up a ton of IPv4 addresses, reducing the need for AWS to purchase new ranges."
Yup, this has been obvious for a while if you read the better economic analyses. Charging for IPv4 doesn't on its own remove it. It creates some sort of economic balance between the value and scarcity of the IPv4 address space.
When you're trying to fit the entire world of 7 billion people into 4 billion addresses, the space looks pretty scarce. But assuming a roughly power law distribution of services and their importance of being on IPv4, as you cut off the people with lower-end needs, like, "my cell phone needs to communicate on the internet so let's give it an IPv4 address", you extremely rapidly cut through orders of magnitude of the old uses.
That long tail of "Facebook is not willing to cut off even .01% of its user base so it has IPv4 addresses to serve on" may take a long time to get through, but we're well through getting huge swathes of the other users off of it.
What kills IPv4 is in the far future when the expense of maintaining it specially exceeds the benefits. Since maintaining it is rather cheap, this is going to take a while. But as IPv4 diminishes in importance, ironically, so does the value of entirely eliminating it. When it is 1% of the traffic, who will really be desperate to drop that to zero?