Even if they'd add Irregular Tomestones to the Mhach raids, most would still avoid those three raids in favor of the Crystal Tower raids.

Labyrinth of the Ancients, and Syrcus Tower are both much easier and faster to clear, which means obtaining Irregular Tomestones faster. It's also rather easy to avoid getting the Mhach raids when queueing up for the roulette, since all you have to do is take off enough gear for your iLvl to drop below i175 (or below i90 if you want to avoid WoD as well).