As someone who uses Facebook messaging for some of these things (not the best solution since the reminders/tasks etc. get lost in other conversational clutter), I think this is a great idea and execution! I would like to see the more practical features expanded on.

For instance, if there's a new todo/reminder/etc. added is there a notification sent out? There could be a problem if one person uses the app updates it a lot and the other doesn't check it as often.