If you want to make an off topic area, there had to exist the topic in the first place. What is actually on topic at LW?
I am not sure whether I support your plan. Perhaps you should write the "off topic" discussion post you want to write, not caring too much about its topicality?
Petition: LW should introduce a dedicated off topic area
Why?
1) I want to discuss various topics with people who are both intelligent and rationalist, and i know of no other place where to do it.
2) If find that rationality is getting boring in itself. I need to use it on something.
3) As stated in this comment http://lesswrong.com/lw/btc/how_can_we_get_more_and_better_lw_contrarians/6e3p
the narrow set of topics might actually hurt LW by driving good rationalists away.