Quickie off-the-top of the head stuff on forums….
1. Ability to easily place banner ads or other things in the forum - even every “x” posts in a thread. Other forums have this (often as plug-ins).....many of us make a living from ads, so they are important!
2. Social media hooks (whatever they are).....
3. Ability to easily archive posts in various ways (all before a certain date, all from a certain forum, etc.) and therefore make the data set smaller and faster for current live data.
4. Any and all image upload and various related simplifications and tools.
5. AJAX and other methods of interacting with the data which appear more modern to the user.
6. BETTER AND FASTER searches and indexing - speed as well as fuzzy logic, etc….
7. Restrict certain actions - forums that new users can post into…until they post X times, etc.
8. Better Documentation of the Forum variables and hooks.
9. Previews of the content of a forum post by mousing over title of that post…..
10. Lots of membership options…for the admin to deal with users. For instance:
a. Delete users who signed up and never posted in X days (years)....or send them an email about it.
b. Remind users who signed up X days ago that they have not posted.
c. Lots of others things I can’t think of right now…..
That’s the one minute quick think…...I would assume that someone from EE has a list of items from the feature request forums….which may relate!
Here are some from the last 3 years…I doubt many have been done yet…..
http://ellislab.com/forums/viewthread/94455/
http://ellislab.com/forums/viewthread/92388/
http://ellislab.com/forums/viewthread/91515/
After all those, there are dozens more that should be considered. A decent way of doing so would be to query members as well as look at other modern forum software (Xenforo, for instance) and see what is being implemented. Realistically, most people need…or can use…most of the same things. Not to say you have to add thousands of features, but the top 20 probably deserve consideration.