I rather liked VMS conventions as it was immediately obvious what was the directory part of the path and what was the filename and the device. You could create virtual devices as well, so for example, with VMS TeX, I had TEX_ROOT defined to point to the root of the TeX distribution and you would have TEX_ROOT:[INPUTS] for the input directory, TEX_ROOT:[MF] for Metafont files, TEX_ROOT:[EXE] for executables, etc. and everything was logically arranged. CLD files were another wonderful thing where you could define your CLI interface in an external file and let the OS handle argument and option parsing for you.
On 2 & 3, what if you have a directory? There’s no easy way to tell whether /foo/bar is a directory or a file. FOO:[BAR] must be a directory.
I have a vague notion that there might have been the ability to have a virtual device span multiple directories, but as I think about it, this seems unlikely since it would make it ambiguous where something would be created if a directory exists in both root1 and root2, so perhaps not. It’s been 23 years since I last used VMS and 30 since it was my daily driver though, so it’s hard for me to say too much.
