So this idea came to me while in the car on my way home...
It's useless, you are free to skip this post if you want, but I wanna share my craziness xD

Okay... laughed enough? xD
Now shoot me xD
Alright, let me explain just in case my thoughts weren't successfully expressed xD
We know Volume 22 ends with Chapter 174, so here I am assuming that CLAMP will keep the 8-chapters-per-volume pace (like it usually is).
So we have 8 more for 23, resulting to 182 chapters, 8 more for 24, resulting 190.
Following me until now? Good xD
On Volume 25, however, there's going to be 9 chapters SO THAT Chapter 200 can be the very first chapter of Volume 26. We know CLAMP would do that... they did it with chapter 100, I think they'll do it again with 200.
So, 9 chapters for Volume 25, resulting 199 chapters plus 8 chapters for Volume 26 (back at the 8-chapters-per-volume schedule).
We are at 26 volumes, 207 chapters, good.
Now, two things might happen... either the 8-chapters-per-volume will continue or both Volume 27 and 28 is going to have 9 chapters each. The latter theory is only because by doing so, the final chapter would be a round number, 225 (which is my guess). Otherwise, it shall be 223 chapters (or 224, a middle-term xD).
Why do I think there will be 28 volumes? I have a lot of evidences xD Just to name a few:
- 2 Character Guides covering 7 volumes each (makes us think that the 3rd will cover another 7 volumes and a 4th and final one, more 7).
- Artbook covering illustrations from volumes 1 to 14 (makes us think that there will be another Artbook covering the illustrations of other 14 volumes).
- Ohkawa stating at Puff's interview that 2/3 of the story had been told by chapter 140.
Now you can shoot me again, for having nothing more useful to do at this hour xD