Hi, i am working in gsoc multiple repository support project
(http://socghop.appspot.com/gsoc/student_project/show/google/gsoc2010/gentoo/t127230759165)
and i am writting to ask for ideas and suggestion for my
implementation.

The proposed project is to implement support for multiple repositories
in sys-apps/portage. Today, portage handle just one repository of
ebuilds, with a lot overlays attached to it. The idea is to change
Portage internals to support a stack of ebuilds' repositories. Each
repository will be a standalone repository and may have overlays
applied to it. Syncing the repositories and overlays will be done
using emerge and repositories will be added in a config file.

I intend to create a new dbapi class to handle just one repository,
without any overlays. This class should receive one parameter in
__init__ with the path of the repository and will implement all
functions of dbapi. Than i intend to change portdbapi to maintain a
stack of repositories (the new dbapi class), instead of the string
list self.porttrees. An overlay can be implemented as a new repository
in the stack. This way emerge and other tools should work with just
little adjustments. I also intend to implement in emerge, sync
functionality to all repositories, not just main repo. And there will
be support for several csvs.