Hello, ghost of Goonmas past here. Just wanted to clear some stuff up. Ignore it if you want, but note that I've long since checked out of the game and have no allegiances or politics to push.
First up, it was very much sincere, and happened long before any "blocs within blocs" came about. We got along quite well with TKR and many of the other Chaos alliances. We wanted them out of the war and would have been very open to working on a "sphere" with them post war. We ultimately worked it out with the coalition that we could extend an offer of white peace to Chaos, but they refused to peace