I think such a repository you're talking about could be indeed a good
idea. But it could have some disadvantages to, like also all those
custom PPA Ubuntu repo's has.
The packages maintained by the Debian Multimedia Team are safe, stable
and have good quality. The Debian packages do pass some quality rules,
which is a very good thing imho, better then having a repository without
any 'warrantee'... Also your idea could have the effect that people only
upload their packages to this repo and not to Debian itself, so there
will be a quality loss...
But for packages which are valuable and do not pass the (license)
criteria of Debian it could be good to have such a repository. For
example for a realtime kernel and stuff like dssi-vst, (FST is a
candidate for Debian imho), linuxsampler (?), Jost...
Also, some developers make packages of there apps themselves. I think
it's the best for Debian (based) distro's that they build it against
Debian unstable, so the community can use it and the package maintainers
can use it to build it against their distro easily.
So maybe some kind of an
- Debian Multimedia 'experimental' repo > for packages build against
unstable, which are not in Debian yet. Devs can upload their packages
to this repo and package maintainers can use it for uploading it to
Debian. (I think if you setup such a thing, it should happen in
corporation and communication with the Debian Multimedia Team!)
- Debian Multimedia non-free repo > for dssi-vst, jost, etc.