The File Filesystem (2021)

Useful enough that it should be an OS-level standard feature, imho.

Unix-like OSes allow mounting disk images to explore their contents. But there's many more file formats where exploring files-inside-files is useful. Compressed archives, for one. Some file managers support those, but (imho) application-level is not the optimal layer to put this functionality.

Could be implemented with a kind of driver-per-filetype.

It exists :-)

For zip archives, there are fuse-zip and mount-zip which are FUSE filesystem.

As an intermediate between OS level and application-level, there are desktop environment level: gvfs for GNOME and KIO for KDE, but they are compatible only in their own ecosystems.