X has been on hold this long because Kadokawa refuses to publish it.
An article a friend sent me says it all on a livejournal.com discussion:
"The awful Truth behind X's pause
I officially hate kadokawa... No, it's not Mokona's disease (gosh, there are people who believed that? Yeah), it's not Ohkawa's lack of imagination (who came up with this should be burned in hell), no it's not Tsubasa and XXXHOLiC (poor kiddos *hugs Tsubasa/holic charas*)... it really is what we feared the most: Problems with Kadokawa
It's official. I was surfing on the internet and I found this blessed page, which is totally dedicated to X's pause.
With the gently help of Sakura-chan and babelfish XD we managed to translate the most important parts and we can say for sure that.
CLAMP gave a long interview on Puff Magazine later on July 2004 (about a year we could have the truth! ;_;) where they were asked about the pause on the serialization.
Ohkawa answered that the magazine is not accepting the end because of it's content. Apparently, is a bad end, aka, sad, bloody, with gruesome (or is it too happy/sweety? I really doubt).
And this is not the first time they "fight" with kadokawa, according to the interview, they also were asked to change Wish's ending. And CLAMP changed it (;_;), and in a hurry to follow the deadline.
Even though the war is set, Ohkawa made clear that they DO plan to publish the end, that even though the serialization stopped, it doesn't mean they'll never do it again."
I give full credit to Yuuto here on Minitokyo for this find. What do you think will happen?