It ended because there's an actual 尻取り game on the site now!
Check it out.
[url=http://www.renshuu.org/index.php?page=community/activities&sid=0]http://www.renshuu.org/index.php?page=community/activities&sid=0[/url]
Just as an fyi, there are many active games of this (including achievements, points, themes, etc.) under the Games section of the menu. This is leftover from when the actual game had not been developed for the site.