Some of the restrictions have already been implemented in macOS 27 by restricting access to (at least some ?) containers even with Full Disk Access on.

One niche issue resulting from this : it broke the ability to access my own screensaver settings and files from it's settings app, because those settings live inside a container for a system extension that belongs to Apple (because Apple still hasn't publicly released it's "modern" screensaver api, it's still old style plugins run by a legacy extension).

Several screensaver developers I know got bitten by this and there's no proper workaround, you just have to use "/Users/Shared" and hope that doesn't go away any time soon.

In my case it silently broke migration for Aerial from 3.X to 4.X in Golden Gate (where I moved away from the legacyScreenSaver extension to the new undocumented wallpaperextension format). I did move to "/Users/Shared" earlier this year but some people will inevitably get caught by this if they didn't update, and there's no recourse, FDA doesn't work, you can't even ask for access, nothing works. And since it's a silent fail, I didn't even notice before this week.