Well... It's not much, but at Computex they said they were working on 1080 card to fit in their eGPU, which is designed to just barely fit their 1070 Mini.
From a
PC Gamer article:
"Gigabyte's mini-ITX GTX 1070 normally sells for about $380 / £350, so the dock adds about $200 to the total price. And Gigabyte told me that a mini-ITX GTX 1080 card is in the works for the future, if a 1070 just isn't enough. Gigabyte says the Gaming Box should be available starting in July."
And from our own James Schell's
article on it:
"When asked if the GTX 1080 would fit, we were told something to the effect that it will soon and that they’re working on it. Make of that what you will."
So... it's definitely in the rumor category, but I bet they do it. The 1080 only consumes 30W more and the 1070 Mini cooler is already very good and quiet, so it wouldn't be difficult.