How easy can it be to collaborate with text files (Markdown) and Git? - and a Git forge? - need to make easy: authentication, permissioning - limit the actions writers can take - list the typical/likely breakdowns in collaborative writing (Git-based) - what options need to be provided to deal with breakdowns?
(in the following, "use a" might mean an external tool, or it might be wiki practices)
FWIW, I think Gitbook has a great model. For simple changes, all you have to do is:
In Gitbook, click "Edit" => Click "Merge" => Changes are synced to the associated git repository OR
In Gitbook, click "Edit" => Click "Request a review" => Reviewer approves/denies => Changes are synced to the associated git repository For more complicated collaboration, you always have the option of using standard git features with the associated git repository. Changes in the git repository are propagated to Gitbook and vice versa.
This model helps accommodate both non-technical users and technical users alike.