I too look forwards to having to manually updated all security patches for each binary in the system.
The fact that things like flatpak, snap, nix all explicitly try to address this problem with platforms/base layers/grafting etc. is very telling. They are all a trade off of your security vs. the dev's convenience, which might be necessary to succeed.
After Silverblue, when they run in Flatpaks, they can still maintain build scripts that achieve the same thing.
The distribution itself can even maintain a common base image for all flatpaks in the official repos, retaining all of the code sharing of existing systems, but with the benefit of a more robust and modular solution when they need to make exceptions. End users will also be able to more reliably use applications that are not supported by the distribution proper.
alias df='df -x squashfs'
Given that squashfs is a read-only filesystem, I don't know why this isn't done by default. No one needs to worry about how much free space is left on an ro volume.
I also go a few steps further and disable udev (-x devtmpfs) and tmpfs (-x tmpfs) as well.
findmnt --df --types