I don't know about module types but as I mentioned before I would like to see new events in the event plugin that run before content is actually saved to the database. For example q_before_post, a_before_post, q_before_edit and so on.
Also another idea that came to me yesterday - I think a Custom HTML Widget would be very useful. I found myself creating some widget plugins just to show basic content in the sidebar on specific pages.
Under Admin>Layout, instead of all the "Custom HTML in..." options, you would just create a new HTML widget then choose (a) what position it would go in (top, sidebar, side panel, bottom, etc); (b) what pages it should be displayed on (questions, tags, ask, etc); and (c) the module content itself. Advanced content like question lists would still need a normal plugin.
EDIT: just thought of something else. I don't know if you are planning to add badges to Q2A natively (if so, I recommend integrating Noah's plugin if possible) but if you are, then some way to extend badges would be great. So you can create your own conditions like "asked 10 questions in tag X" or whatever. That might be quite a big task though.