Is it only me or does HBM2 look like it wont be the magic thing giving AMD any meaningful edge against NVidia? The next NVidia cards (soon^tm) probably have like 12Gb GDDR6, which will offer more capacity at faster speeds than HBM2 for Vega? Not that I knew anything about graphics cards memory in detail...

It's not only you, but HBM does have very tangible real bandwidth and latency advantages. It's no luck that NVIDIA is using it wherever they need real performance (see the Tesla cards).