I think that the interesting part of these things is the actual posts and the responses to them, not the votes. I think it should work more similarly to CMV (Change My View) on Reddit. Have a thread (maybe just the open thread) where people are encouraged to post where the say something that the expect many people on Lesswrong might disagree with, and people try to convince them.
I also think that the value of the votes is much better if there are upvotes and downvotes. Unfortunately this could be bad for karma. Perhaps each post should have a poll in it, and people upvote just based on how interesting the conversation is.
I also think there was a problem with people posting underspecified claims. Words like "feminism" and "can" have many sometimes contradictory definitions.
I like the suggestion of using a poll, but that is even harder on the poster than adding the special notice. Also: The karma-incentive on contrarian ideas is beneficial.
I'd like to use this thread to review the "What are your contrarian views?" thread as the meta discussion there was drowned out by the intended content I feel. What can be done better with the voting system? Should threads like these be a regular occurence? What have you specifically learned from that thread? Did you like it at all?
Usual voting rules apply.