The only purpose for this that I can see is getting the non-serious stuff out of chat, comments, Programmers SE and Meta SO. This would be a lose/lose situation, because
- the only value in the sites comes from getting all the non-serious stuff moved
- you'll never get all the non-serious stuff moved, so there's no value to be had
- by eating up people's time and energy for no useful purpose, these sites would actively hurt the "real" sites
- the people who do play along will get annoyed at people who don't, and vice versa; we already have one eternal war going on courtesy of the subjective/objective camps, we don't need another one
Not to mention that these sites wouldn't exactly be making positive contributions to the general fund of human knowledge. And yes, I realize you initially proposed this before chat and Programmers existed.