The beauty of that feature is the system to implement it - extfs(EXTernal virtual File System) - is built with simple scripts, so you can add your own little tools to make other things navigable beyond the ~40 that come bundled.

There is a simple introduction in /usr/lib/mc/extfs.d/README, or https://github.com/MidnightCommander/mc/blob/master/src/vfs/... .