I would suggest a feature that give any WordPress blog owner the possibility to set up discussions where participants publish posts by turns. This can give to the reader an ordered and equal alternance of the reasons and points of view of all participants. And also give to each participant more time to examine what the others write, consult documentation, receive suggestions and to think about the appropriate replies.
This render it a valid tool especially for debates about any type of disagreement/controversy or between candidates to any type of position.
The system may work as follows:
The blog owner can create one or more discussions.
For each discussion he can admit or invite the participants he want. He set the time limit, that is the time each participant has for publish before miss a turn. He can also set the maximum length of each post.
Thus, there is a list of participants. At the start, it's turn of the first of the list to publish a post. The others aren't able to publish until he has done or the time limit pass. If he don't publish by the time limit, he miss a turn.
Next, the turn shift to the second of the list, that can receive a notice by mail or other. And so on, until the last participant. Then the cycle restart.
The blog owner can add, remove or block partecipants, or can even block the entire discussion, forever or for a certain amount of time.
Each participant can remove himself, or simply block temporary if he can't partecipate for a period.
Apart this procedure, all other features are like a common blog, depends on settings: it can be public or private, readers can contribute via comments or not, there are the usual systems for stay updated (mail alert, rss, etc.).
Readers could also have the possibility to vote for the participant whose posts they prefer.
It could be the possibility to vote the discussions across the entire wordpress.com, that could have a section dedicated to these discussions with lists of top rated and most followed, lists by argument, tools like search, etc.