The NDA has finally been lifted and here and there one can find benchmarks for this card.
Apparently the Fury X more or less matches a reference 980Ti in 4K (or UHD-1 for you '3840x2160 is no 4K'-nazi's) resolution benchmarks, but drops the ball in more 'playable' resolutions like 1920x1080 or 2560x1440. The latter is presumably because of AMD's notorious driver overhead and might improve in time/Win 10/DX12.
The cons are that it's no 980Ti (or Titan X)-killer, only has 4GB of VRAM (if 4K is your main goal, then 4GB would be a bit on the low side, even though there's plenty of explanation for it because of HBM-1 limitations), doesn't come with HDMI 2.0, and neither a DVI-port (in both cases one has to buy an expensive active adapter to fully support both interfaces).
It's currently priced at starting at an absurd price of €780,- ($871,71, over 200 dollars more than the MSRP) in the Netherlands (and not yet available), while the cheapest 980Ti's start at €750,-, and have a better availability. In comparison: when the 290X was released it's cost was below €600,- over here.
Personally, if I wanted/needed a new high end videocard right now I'm not sure I would have gone for AMD this time. Not that I currently require an upgrade.
I can't say that I'm actually impressed. But it's just my opinion!