Kanban = flow
Thanks all for the thoughts. We've adopted the kanban system into our GTD practice - and it really is about flow - or as stampf articulated it - it's a tool to reveal problems in our work flow. It's been helpful so far to keep pace, communicate activity to other teammates and most importantly - point out when there's too much or too little in the system. This makes for a better weekly review process.
I think the main benefit of adopting the kanban system reveals itself in team dynamics - where someone can quickly take a look at the system and see 1. what each person is doing 2. what is left to do and 3. progress as a whole.