FWIW CPAN works like this. A "namespace" (eg. IO::Foo) is essentially assigned to a user and only they can upload packages in this namespace. [http://www.cpan.org/modules/04pause.html#namespace]

Also it's very common in distros for maintainers to be granted only access to a list of packages, which is similar to what Ubuntu is doing here (and indeed already does). In the distro case, the maintainer is usually different from the principal developer of the program.