Thanks for this post, I appreciate your help in making this important step more visible to the community!
For more context, I can add that we decided by looking at the data from our active user base, where the usage of older PHP versions is definitely smaller than the numbers above. When it decreased below a certain threshold, we introduced a notification in Yoast SEO 19.12 last December, urging users on 5.6-7.0-7.2 to upgrade by the following March.

Even if the impact for us is limited, we really hope our move can be instrumental in moving the WordPress (and the web) ecosystem further, there’s still a lot of work to do and we’re trying to do our part.