I think that collaboration means not just track changes or comments, but primarily good and almost-native roundtrip with the major wordprocessor (word). I thought that one of the strengths of switching to xml was that it would allow to advance in parallel on communication with other formats without having to rewrite the wheel every time. The developers could even outsource that functionality (that is, hire somebody external to create professional filters) without diverting them from the core programming.
Track changes and commenting (badly needed) without communication with Word (and perhaps openoffice) users does not sound like a good deal to me.
Mellel 2.7 around the corner...
Moderators: Eyal Redler, redlers, Ori Redler