polaris success will be the price point, if they are even a little bit greedy, it will turn into a failed product, but if they can bite their arm for a while longer and deliver a great price they might even take ppl away from the 1070 and market share, afterward they can charge better margins for vega.
Pricing is difficult though. If they get too aggressive in going for low prices then with minimal margins then although they will claw back market share their budget for future R&D just gets smaller and smaller. I think they need a price that maximizes profit, not maximizes market share. That doesn't mean selling at high prices, just not rock bottom. AMD have mentioned this before that they need to loose their budget image.