Regarding the effective monopoly on high end, this will change next month with release of Vega card.
And AMD will have again a very expensive card to manufacture GDDR5/5x vs HBM2 with high power consumption based on the fact that the RX480 draws nearly as much power as a 1080 atm, and HBM2 isn't exactly power efficient (unlike HBM1 vs GDDR5), HBM2 is nice but the power requirement currently increase with the density, and it leaks voltage pretty badly with 4 stacks...