Last time I experimented with Gentoo-Prefix is about half a year ago. I don't know what type of problems I had back then but I remember I did not get far enough. Now - as I'm finally having a tiny bit of spare time for Kolab/Horde again - I did actually get it to compile and run. Nothing more than the base install. But I didn't see anything that would prevent me from trying to get a Kolab server running in such a prefix.
Combine that with the fact that the Kolab server is currently searching for a replacement for OpenPKG... ah, a tiny tiny little wee bit of hope. I don't think it will work out as I would like it to but at least I'm trying.
I believe the Kolab crowd will prefer a native installation method as their next primary platform. But OpenPKG had some significant advantages - even though nobody liked the distribution itself.
Gentoo Prefix would allow us to retain these advantages. Ah, back to playing around...