Alright, I've tried drafting a response three different times, and I've liked none of my drafts so far. However, I think I can't wait anymore to get the wording right. The teacher perspective needs to be interjected now:
My initial reaction to this idea (last week) was that maybe we are starting to get confused about the types of communications that belong in the new comments exchange option in assignments (which I guess I had defined in my head as an area to exchange short "tweets" of sorts and nothing more) and the more involved feedback made possible by the file and overall assignment feedback options.
I also find that I've been asking myself the following question a lot these days: At what point do we end up giving our students feedback overload? And how do they know where to look at any given time? It gets a little overwhelming to track all of the different ways we've created to leave messages for one another in our courses. It isn't just in Moodle, either--it's in other systems, too. Take the Turnitin.com integration, for instance. I can post general essay feedback. I can post specific flags with comments directly on the essay. I can post recorded verbal feedback. I grade with the rubric, which also provides a kind of feedback. All of these options are pretty amazing and give us opportunities for a depth of exchange we haven't had before. So I'm thinking to myself, I'm providing a pretty high level of feedback, right? Until I get an email from a student saying she thinks I probably left some comments somewhere, but she can't figure out how to access them because no one yet pointed out to her what the icons mean or she didn't yet access the "How to access your instructor's feedback" tutorial prior to looking at her draft. Upshot: What good is having all of these options for communicating if the message doesn't get to the recipient? And should my student have to access a tutorial first before she can access her feedback?
Specifically, with regard to the comments option, I'm finding that while I REALLY like the two-way communication option, it is so easy to miss that someone said something if one doesn't have the arrow activated or isn't paying attention to the fact that the 0 has turned into a 1 or 2. I am on board with the idea of creating a more robust two-way conversation area than we currently have, but I'm not sure whether opening up the comments in this way would just exacerbate the multiple feedback loop issue if the definitions of communication purposes aren't more clearly drawn up first--or if something doesn't get streamlined somewhere. The flexibility of the proposed options in the settings area sounds really great until I start seeing how many switches I will have to remember to throw or not throw. Please, please don't direct me to the messaging options window for any other settings options. My own eyes glaze over trying to navigate all of those decisions, let alone a group of teachers or students who are brand new to Moodle.
I'd therefore like to ask us to take a step back for a moment and ask ourselves if we are asking the right questions. I think you ARE asking the right question where you begin your conversation here: how can we create a space where teachers and students can have more robust communication? It is in attempting the execution of a solution that tries to use a system with pretty inherent limitations that I think you start to ask the wrong questions. I've been watching the developments in outcomes and elsewhere starting to take shape, and I'm thinking we are coming closer than ever before to being able to offer a more cohesive, meaningful, dynamic learning environment that is a curriculum map, portfolio, and highly personal learning space all at the same time--but we keep chopping this experience up into little pieces as we come to understand the smaller parts involved in this endeavor.
This has been the vision I've been chasing ever since 2008 when I first looked at outcomes and assessment feedback options in Moodle:
In a perfect world, as a teacher, I want a system that dynamically maps my curriculum as it grows and adapts to the learners in my courses as they come in and out of different collaborative groups and individual projects; as a learner, I want to see a portfolio that shows my growth over time--and shows it by capturing the snapshots that have been most meaningful to me. We are closer than ever to being able to offer this system, and that is really exciting to see.
Now, when you meet on the 26th, I respectfully ask you all, as my favorite educational software wizards, to try to move forward with the idea that this system needs to function as a cohesive whole, no matter how many chaotic and disparate things are going on behind the scenes. One way I see this happening is if, somehow, we start to think of tracking these systems differently--maybe having systems that work in parallel and often together at given points without being inextricably bound to one another: a learning object that can have comments/feedback conversations attached or not, grades and/or outcomes attached or not, in a portfolio--now THAT would be a powerful tool for a student to control and wield. I'm not sure if that is what you meant, Martin, but if it is, it really caught my attention.
And Jason, if you are starting to envision a commenting ability that might replace the other options causing the feedback loops I described, so that all of the feedback related to a learning object starts getting logged in the same place--then I am liking that conversation direction, too.
Back to the how: You know I have no business talking about the how, really, so I'll just leave that part of the discussion to you with one plea: Whatever you all decide to do, make it so that it is something simple that can be done in very few steps with no extra settings and no complications involving decisions that a site admin has to make when it really is a question of individual preference on the part of the teacher.
Finally: THANK YOU! I like that you are still starting the conversation with what best promotes a richer learning experience. 
