On macOS, there's something which I think is called a "bookmark" these days but which used to be called an "alias", and it's used to record a reference to a file. It's basically a data structure that contains a bunch of metadata for a file, so if the file moves, there's a fallback process which locates the file and updates the data structure with the new metadata. It's fairly simple as you'd expect, although it's much more than just an inode. The data structure can just be an object in memory or it can be serialized to a file on disk.
You could implement this yourself on Linux, for sure, but it's been around on macOS since System 7 appeared in 1991 and everything uses it.
With 2 and 3 - yes you're right I didn't realise that was how it worked on macos! Those are both interesting features I haven't seen elsewhere. Although I think 3 would be possible to implement say in gedit, as the inode of the file you save shouldn't change when you move it in the file manager, everything in Linux is usually path-based so this might be kind of unexpected.