I have been working on a SOGo package and module. It was not easy to work my way through the seldom used GNUStep framework and its integration in nixpkgs, but I was very impressed by the work performed by @matthewbauer and possibly others. Many thanks to you, and possibly them! It is an impressive piece of patches and workarounds to make GNUStep go along with nix constraints.
As I invested quite a lot of time in this (see the diff), I wanted to at least inform you that it exists in the hope that it will be useful to someone. With the above work, it is possible to start a working sogo frontend. The remaining integration steps wit an imap server and ldap server should be configuration only.
I am available to discuss with and help anyone interested in this piece of code.