The DDs who work on, say, kernel packaging are not necessarily the same DDs who work on Wesnoth packaging.

For one like the other comment pointed out different people internally often already work on different packages.

For the other external repositories are a thing.

But they are often not trusted, and if a package is maintained by upstream often it is only for one or two repos.

So it fix it you would need a repository which can work across distributions. Where maintainers exist independent of the distributions but also the organization is big and reputable enough so that people do trust it.

But to have that you need to use technology which abstracts over differences in distros especially wrt. .so dependencies. Like nix, flatpack or snap.

Or in other words I believe you either have what we have today. Or you have a core OS (which still needs packages and package managing!) and the rest is using technology similar to nix, flatpack or snap to provides package repos across distros.