I mean there are better tools, such as TMSU or tagfs, which i think are actually better approaches to having (part of) your file system displayed in a non-hierarchical way - or rather in a dynamic hierarchy.

But the other poster is also right in that for your system file system, i.e. root and operating-system critical paths, do not benefit from such an approach. I think asking for such a thing kind of sounds like an XY problem and requires listing the actual problems to solve with an alternative approach first.

If my grandmother had wheels, she'd be a bicycle. Don't try to force a hierarchical filesystem into other applications. Asking "what it if was different" doesn't make sense, because if ext4 was a tagging filesystem, it would be tagfs! Tagfs and others already exist, you can use them today! Go crazy, use object or document stores! Embed everything in xml! But for operating systems or actual human interface, those are terrible ideas, which is why we don't do that.

I brought up hard links to say "yes, you can do that, but it doesn't mean you should". There are few cases for hard links. The only one I've seen in actual use is in media downloaders, where a file gets downloaded to one folder, then hardlinked from a library folder, so that you don't have two copies of that video. The library (jellyfin) can do whatever it wants to the link (move, rename) while the downloader (qbittorrent) can still keepit for seeding, and either side can happily delete its copy without affecting the other.