This proposal is a very far-reaching proposal which started from the discussion about OrphanedPackages and which has been discussed IRL during the QA meeting (see the videos here). Everybody interested by this proposal is welcome to join the collab-maint-devel mailing list.
Collaborative maintenance means using a Version Control System (VCS). Subversion being the most popular choice nowadays, we'll use this one as the basis of this proposal. However the infrastructure must be designed in a VCS-agnostic manner: it must be possible to write modules to add support of other VCS.
So the main part of the infrastructure is a subversion repository. Packages are handled like usual with svn-buildpackage in their own directory. Up to now, this is nothing new as many people already do it. We need to add meta-information in the repository and provide several services to ease the work of everyone.
Since we want to open the access to many external contributors, we should be able to restrict their access to the packages that they are interested in. Of course the ACL (Access Control List) must be maintained by a group of trusted developers. This Wiki page explains how to proceed to set ACLs.
Is the version in the repo newer than the version in unstable/experimental ?
Output of pbuilder run ? piuparts ?
For example, it should be possible to configure the infrastructure so that each SVN commits sends a mail with the diff to the Package Tracking System.
Also, the system should follow uploads made to unstable/experimental and check that they come from the repository. If not it should reintegrate it in the repo. It should also inform the maintainers about this (unfortunate) event.
For beginners who are not ready to use SVN yet, we may have a Dak install so that people can upload sources packages which would then directly get injected in the repository (idea from [NeilMcGovern] reformulated by RaphaelHertzog).
Ubuntu is currently working on a tool called REVU which helps reviewing the packages from external contributors. See the specifications in particular for good ideas.