If the rumours of the RX 480 performance is true, then it will sell in much higher quantity and faster IMO.
I very much doubt it. I've only bought AMD GPU's for the last 10 years for my desktop PC, and I've ordered a 1070.
NVIDIA have the market locked up, there is no competition. The 480 will most likely be 970 performance levels, that isn't even that exceptional for $200, it's good news for sure but nothing earth shattering.
For those like me on a 390X there is no upgrade from AMD at the moment. Well unless you want to buy a 4GB VRAM Fury in 2016, which is a pretty dumb idea as it already runs out of VRAM in some games.