A lot of people have been asking for better image controls so I think what would be great is a more general image upload plugin/API. I see there is qa-wysiwyg-upload.php in the WYSIWYG editor plugin - if I was to use that for the Markdown editor I would be copy-pasting a whole bunch of logic and permissions-checking that could be done automatically in the core. This could then be used by any plugin, say a plugin to allow a user profile image or whatever.
Also along with this it would be great to have an option to upload files to the filesystem instead of the database (e.g. a qa-uploads folder, perhaps structured by month/year like Wordpress). Also, resizing images.
Q2A is getting targeted by spammers now so I think some better spam control is necessary. A few options to consider:
Run posts through Akismet.
Allow admins to specify keywords to mark post as spam or send post for approval (i.e. instead of having to create a plugin).
Addition to the filter plugins to be able to send a user account for "approval" - e.g. if multiple accounts sign up from the same IP or the username/profile contains certain words.
Regarding the My Updates: it would be good to have an icon at the top that shows a number of replies/messages you've received, like on forums. Something like this. I would not include "updates to favorites" in that number, just post replies, private and public messages. On this subject it would be nice if private messages worked more like forums too. We have the PM store, but it only shows when you go to send a PM to that user. A basic page listing all recent PMs would be better IMO.
Can we also make the censor apply to user profiles as well as regular posts? Plus the public/private messages of course.
Edit: a request from my users - listing the exact join date in the user profiles. "2 years ago" is quite wide-ranging. I'd suggest something like "Member for: 2 years (joined 01 Jan 2011)"
The ability for plugins to list privileges on a user's page would be a bonus, for example "Banning users from chat" or "Creating new tags". In fact, hooking into most tables in Q2A is a PITA.
Also on the subject of privileges, I just found that only admins can edit user profiles. It would be nice if we could set that privilege and give it to moderators too.
May add more later if I think of anything...
P.S. it would be nice if you added my User Activity Plus plugin to this site, or made it core... I'm constantly trying to find old questions/answers I posted here ;)
P.P.S. It would also be great if you committed more frequently to the git repo. You can set up a branch to do 1.6 work on so that the master branch isn't polluted with incomplete code, then merge that back in when complete. Would also allow you to accept pull requests for bug fixes etc. Take a look at http://git-scm.com/book/