Personally I think Nix (https://nixos.org/nix/) does this right: packages are easy to install and upgrade for users, and developers and maintainers can easily create and update them. And if someone does not like the default collection of packages, it is as easy as starting one from scratch, or forking the existing one on GitHub, but at least it doesn't require reinventing the entire system.
The base problem is not ISVs or maintainers. But that the rigidity of the package managers force maintainers to either use one version of a lib for the duration of the distro version, or play musical chairs with the package names to get around conflicts.
Either option makes it hard for third parties to produce packages.
The likes of Nix allows multiple versions of a packages to exist side by side, and ensures that each program gets the version it wants.
This allows a third party package to request a newer version of a lib than the distro provides, as it will not conflict with the distro provided packages while retaining the naming scheme.
I second this. I'm using Guix both privately and at work to provide bioinformatics software on our cluster. We have an additional repository of package variants for things that shouldn't be part of the default collection.
Writing package expressions is usually very simple, especially since we can use package importers to automatically generate and update them.
