How about a junction link? Currently a link can hold a $PATH,
but it`s dead as it`s not recognized ( by the kernel or FS ? ).
A link`s much simpler and less kernel intensive than mounting.
All paths in the link`s $PATH would be visible and readable.
Path precedence handles duplicate dirs. and files, no white-outs.
But only the first path in it`s $PATH could be written to, but
if it`s read-only or not enough space is available, then error.
This would allow a CD + writable layer on top to work properly.
Also possible, writable junctions on dirs. inside Squash files.
# A sym link can already hold a $PATH, why not make it functional?