It's guesswork. Somewhat reasonable with GP102. I expect the same, perhaps 3584 shaders on the Ti if they want it to be as close as the 980 Ti was, but I wouldn't be surprised if they slightly increased the gap.
But you KNOW it's guesswork because GTX 1060 as GP104 1280SP is laughable. They will not cut the GP104 50%, they will have a new GP106 or whatever. Even mobile GM204 was never cut more than to 62.5%, which would match a 1664 or 1536 SP GP104. Expect a mobile part there, and possibly a 1060 Ti there if AMD's pressure is real.
But man, what a joke to even humor the thought of a 1280SP GP104, let alone write it in a chart. Get real.