It's all the "What ifs?". I'd just accept that whatever you buy there will be a better value option in a year anyway.
Although I cannot say Vega won't bring a GPU equal to a 1070 @ $100-$150 less I really think that is highly unlikely, it would undermine the 480. I'm also sceptical of Vega, AMD have been loosing market share, they have left the high end gpu market wide open and currently anyone with a high end Freesync monitor can't buy a current generation GPU sufficiently powerful to run it properly. That has got to hurt both AMD and their loyal customers. The question that leaves is why is it taking so long to close that gap? This I don't know but it leaves me sceptical.