Nix/Guix seems like the only one that's trying something different enough to address some of those other use-cases, but the cat's out of the bag for most people.
I argue that's simply not true. Scripting languages came up with package managers because the largest platform (Windows) does not have a package manager. Actually that scripting languages implement package managers is a very good argument that their functionality is desired. As a side note, every language package manager is much worse in my experience than all of the system package managers I ever used.
I think "largest" is quite an exaggeration since historically scripting languages packaging has been rather terrible on Windows. While Windows was a consideration for languages like Python (I've read they avoided Make because of Windows), for me cygwin always coming up along with it until recently.
Maybe that's because nix and guix don't interop despite having rather similar principles, and because we mostly don't have GUI for it (like GNOME Software has integration for flatpak) nor desktop integration (like AppImageLauncher). Are you aware of work being done in this space?
All I was saying is that if a new package manager addresses all of the issues scripting languages had, scripting languages would still use their own package managers. Because the culture is now set, even new scripting languages would write their own package managers.
The baseline tools, like all the GNU standard Unix tools, and other command line tools are still managed by DNF, APT, whatever, and then another set of apps are managed by Snap. It's pretty confusing, especially if you never use the "app stores" otherwise. You quickly end up with: apt install <some command line tool> and apt install gimp, but now that's a different Gimp than the one in App Store. You also can't really remove Gimp from apt, because it's weird that apt can't install everything.
I haven't really used Flatpaks, but Snaps is confusing (to me at least), because it's doesn't actually replace APT and pollute the output of "df" and "mount".
I'm also concerned that some packages will never be updated, or stuck on a library with security issues. Perhaps that me, but I'd rather that that one application breaks.