No I don't expect the 1070 will cost $300, but why should I? $300 is not the traditional price point for GTX x70 GPUs, $400 is (the 970 is an anomaly).
And you clearly don't have a clue what people will or will not buy. Nvidia has never provided anywhere close to a 55-60% performance increase with a GTX x70 card, generally the increase has only been 25-35%, and yet Nvidia has sold tons of them.
99% of people didn't buy an 8800 GT
99% of people didn't buy an HD 4850
99% of people didn't buy a GTX 460
99% of people didn't buy a GTX 970
In other words saying that 99% of people won't buy a product as niche as a dedicated GPU is pretty meaninglessness.
At the end of the day, Nvidia doesn't really care how many people buy their GPUs, they care about what kind of profits they can make. If they think they can make more money buy selling fewer but more expensive GPUs, then they will do so. Love them or hate them, I would never bet against Nvidia when it comes to business decisions.