X not being finished not Clamp's fault?
http://www.livejournal.com/users/chibiyuuto/28266.html
According to this, apparently the reason that Clamp hasn't finished X yet is because Kadokawa didn't want to publish the content contained in the planned ending. While this was taken from a Japanese website, I can't guarantee that this is the reason why is't been put off for so long, but it sounds plausable. Yami no Matsuei's creator was having trouble with her publisher, last I heard, and was apparently the reason why we haven't really seen much of it in the past few years. It also explains why Wish's ending was so wonky: apparently the publisher wanted them to change it (then again, CLAMP has mentioned that there was a lot they would have liked to have done differently, due to their deadlines and how behind they were on them, so the oddness I found in Wish might have just been due to that). But again, can't guarantee the source, yet it kind of explains a few things... and then, there are other things that don't stack up. For instance, I can't think of what could be so objectionable to the publisher that it wouldn't be published. It can't be gore; for the love of god, most minor characters end up exploding or get cut up into various pieces, and two major characters have already been killed off in fairly graphic ways. So...
It makes me wonder if X's planned ending has something to do with something very, er, "X-rated." Yes, this is the most asinine thing I one could think of, but it wouldn't surprise me. Who knows. Maybe Kamui and Fuuma resolve their differences in the bedroom and give the fangirls what they want. Or something :P.
But seriously, this does make sense, as I've been hearing about all sorts of issues Clamp has been having with Kadokawa (in particular, the artbooks). So it looks like the last three years, Clamp was battling with Kadokawa over how they wanted their series published and distributed.