Thanks for putting this together! This is an important matter so I'm pinning this thread for visibility.
On a personal note I'm definitely downloading my itch.io library - while none of my games there should fall under the current purge I'd rather not risk it. Steam should be safe as, as far as I know, they don't really have a tendency of removing purchased games from people's accounts (even when delisting titles) but I guess we'll see.
Besides the obvious issue of having to keep constant vigilance about our freedom it's also a good reminder to keep backups of anything you don't want to lose access to. It's the only way to be relatively safe from things like this.