This card was always coming no matter what performance Vega is at. Remember these are full chips which would have been manufactured since the start. What else were they going to do with them apart from this.
They could have still used them in the existing 1080 Ti and Pascal Titan.
Remember with Maxwell and the arrival of the 980 Ti, NVidia sold practically zero Titans so all the unsold full fat GM200 chips would have gone into the 980 Ti.