Phase 3 of the Open Government Dialogue here in the US also used
MixedInk and your post confirms a lot of the feedback I heard at the
time.
More and more, I tend to believe that a better approach to
collaboratively writing documents of this kind (where it is essential
to synthesize a lot of previous, often divergent input and/or agree on
commonly understood language for complex topics) is to iterate between
a small group of expert authors and a larger group of reviewers.
A pretty good example how this process can work is the crafting of the
Public Engagement Principles document led by NCDD earlier this year
(
http://thataway.org/pep). It took a team of up to a dozen or so core
editors and maybe four or five iterations to arrive at a version that
mostly everyone could agree on. To be fair, it's worth mentioning
that there wasn't much disagreement about the general direction this
document should take, and the core editors are all trusted members of
the community. So even though that may not always be the case, it
seems the process would generally be more efficient.
Tim