Since the GTX 880 looks like a disappointment judging from the leaks, they could just make the Titan Z into a 790, essentially, but with more VRAM and lower the price than the current robbery.
Also, since they are giving themselves ample of time, until the end of June, they have the time to do that(and who says they couldn't delay it a few more months if need be, they've already did it twice).
So, the new, much more 790-esque Titan Z would essentially be Nvidia's performance crown with a more reasonable price and whose launch would coincide with that of the GTX 800 series to soften the inevitable blow of disappointment among Nvidia's fanboys of the gimped GTX 880 card.
We know that a full GK110 core is faster than a full Hawaii core when you overclock it under adequate cooling. So it will end up being faster than 295X2 if they give it much better cooling, very high overclocks, and a more reasonable price.
Because who really bought the excuse of "driver optimizations" to begin with? Congrats to AMD to forcing Nvidia back to the drawing board. This is what competition should be all about. Now I just hope they can do the same with the R9-300 series coming out this fall on 28 nm, by limiting Nvidia's well-known greed and prevent them from overcharging for a mediocre card that GTX 880 will most likely be, like GTX 680 was over GTX 580.