Look what NV did on 28nm with GK110 (high compute) -> GM200 (low compute focus on gaming). I would guesstimate that with 610mm2 die size, they will repeat the same strategy with GP100 -> Volta. Being stuck on the same node means to get another 50-75% boost probably means going all in on lean gaming focused Volta. Then GP100 would serve as their compute backbone until 7/10nm. If they create a straight up FP32 gaming Pascal, with the performance characteristics you describe, they will have nothing to sell during Volta generation.
This could also explain the aggressive 2017/2018 span between Pascal and Volta. NV could neuter compute and improve the architecture. Pretty surprising turn of events after some people were predicting 3500-4072 CUDA GP104. This means if GP104 has 3072 CUDA cores and it overclockes better than GP100, the gap between them could be 25% or less. A max overclocked Titan X/980Ti smashes 980 OC by 30-40%. Interesting times ahead.