A Chinese website is now writing that yes, Titan is coming out very soon.
May 8th to be exact.
And the reason for the mini-delay? They say it was the drivers.
Furthermore, they also claim that Titan Z won't be as gimped as many thought it would be. The boostclock is supposedly capable of going up to 1058 MHz, a significant boost from previous leaks.
All this was intermediated from Wccftech, so all caveats apply.
Source
Even if the official reason is drivers, it could well be that Nvidia took it back a few weeks before launch to boost the clock speeds after 295X2 came out.
Now TitanZ may indeed get the performance crown, for a salty 3000 dollars. Oh, and on air cooling, too, lest we forget.