Today Ricardo Rocha found an interesting comparison of the comercial product OXF with Cocoon.
It seems to provide some more features like Cocoon.
Stefano already commented on it in November 2002 and said, that their architecture would not scale. Game over.
Perhaps at least it might push Cocoon a bit forward. A little competition never hurts.
The Cocoon Wiki has a page with similar servers to Cocoon.