

I’ve tried setting up projects that used hard links like that and there are some pros and cons to this. On the plus side, you can delete from one location and the file is still available in the other without having to manage a separate repository structure. On the down side, most software cannot copy the structure correctly to a different file system (even one that supports hard links), which can make backups and migrations annoying to deal with – generally you end up with multiple actual copies, ballooning disk space usage and sometimes causing weird issues if the two files linking to the same data (rather than just having copies of the same data) actually matters…
I’d recommend sticking with the “primary repository of real files” and “multiple views filled with symlinks” structure over hardlinks unless you’re really sure you know what you’re getting yourself into.
In principle, sure. I’m not aware of an existing out-of-the-box solution that’d do what you want, but it also wouldn’t surprise me terribly if someone’s cobbled something together to do this before.
If I wanted to make something like this personally (and couldn’t find an existing solution), I’d start by doing some research into PBX software like Asterisk, what derivatives and extensions people have made for that, etc. – being mindful that I’d likely be digging into a deep rabbit hole…