Thumbs up to this question. Most articles I've read simply quote the same thing that's stated on the Google support page.
I did log into my accounts and saw that there is a "Do not automatically expire" option, so is this option going away after May 25th? If not, my assumption is that this is an update to give account owners a way to manage how long user data is stored in order to meet/resolve potential data compliance issues.
It also notes that this update will not affect aggregate reporting, so I'm wondering how this will affect things going forward.