If the 1060 is ~50% of a 1080 in terms of performance, that would make it a bit faster than a 970, and 970s sell for 300 euros now, so a 300 euro 1060 would be a very minor gain in price per performance.
Actually you can get an R9 390 for 300 euros right now, so the 1060 might bring no improvement in price vs performance at all. It would have much better performance per watt, and better VR performance once SMP starts being supported, but I think most people care more about price per performance for non-VR games.