When we say king we mean the best value for the money. Although the GTX 1080 is without doubt the best single GPU on the market I don’t believe it will be the most purchased. Yes, people want the best but it doesn’t make much sense to pay 700+$ when u can get the GTX 1070 for 400~$.
The gtx 1070 offers a lot for the money as we all know the it’s the heir to the 970 which revolutionized the market. With the 1070 you get a lot of performance for your money and i mean A LOT. You can play 1440p very comfortable and it doesn’t get hot as much as the 1080. If you already own 980Ti there is absolutely no need to upgrade as the difference between the 1080 and 980Ti is not a lot.
Now, when we talk about upgrading we must mention AMD RX 480. A card for 200$ and with performances(rumored) about 390x and above. We still need to wait for all the card to hit the market as they are hard to find now but we can expect at Q3 of 2016 to announce the winner but we can all guess from even now, the 1080 will be the enthusiast card if you want to push for 4k, the 1070 will be the sweet spot for 1440p and AMD RX 480 will be for comfortable 1080p gaming.