The problem on Linux is that hard links are exactly what you don't want.

If hard links from the get go were copy on write, then I suspect content defined storage would've become the standard because it would be easy.

Instead we have this construct which makes it hard and dangerous (hard links hide data dependencies) on most Linux filesystems and no good answers (even ZFS can't easily handle a cp --reflink operation, and the problem is it's not the default anyway).

Use either symbolic links (which is fine in most cases) or overlay filesystems. I agree that hard links are usually not what you want.