Not likely as small Pascal will be a very poor side/upgrade on TitanXs.
Big Pascal is where the real action is going to be with performance 1.8x as much as a TitanX.
Well small Maxwell bested large Kepler, although not by much and that was on the same 28nm process. I think that even small Pascal, with a node shrink and HBM2 should be a decent amount faster.
I still reckon NVidia will surprise us all and launch the Pascal Titan first, but probably in limited supply, just to show us that the future is going to be very right indeed. Of course it will be frightfully expensive.