Ciaran McCreesh wrote:
> For future EAPIs, we can have the package manager define
> super-magic/thing-i-use-to-unzip.

++

> 
> One could argue that having package manager support for extracting 7z
> is also not sane, of course, but that's something we're stuck with in
> current EAPIs.
> 

Or we could allow users to decide for themselves with IUSE="7z" in the 
package manager ebuild.  Granted, it would be a bit of a pain predicting 
what formats your package manager will need to handle.