As an Audi Q7 owner since its inception in 2006, I love the Crossover. It was based on the Audi A6 car chassis and handles like a car with the space of an SUV. In a pinch one could use the standard 3rd row seat for SMALL adults or children. Mine have mostly remained folded.
I was looking to up-grade to the next generation Audi Q7, but it was delay several times, and the only option was to buy another one similar to what I owned. Theoretically, I would drive off the lot with a similar Q7 an a payment book as the main "upgrade". Therefore I opted to wait till the rumored 2013 refresh that was moved to 2014 with the e-tron version later in 2014. Neither occurred the design was rejected by Germany. So I reserved a Model X thinking could make a comparison between the Audi and Tesla before committing to either. Finally, Audi announced the 2015 model of the Q7 with the e-tron hybrid (Porsche hybrid technology) to follow in 2016. Keep in mind, when Audi announces a vehicle in the US, it is similar to Tesla announcing in Australia --down under will get one about a year later. There are no 2015 Audi Q7 in showrooms. Each of the US regions will get a launch event sometime this year, a demo (can't be sold) with shipments most likely in 2016. I have to admit, Audi knows how to launch a model and drive interest -- I have been to several and ate and drank to my delight. Sorry for the long-winded retort, but I thought some background beneficial.
My point is if Audi is making a BEV in 2018, their track record for slippage is no different than Tesla. I would not expect any deliveries of the Q8 before 2019-20 in the US. Audi spent 3 years mule testing (to their benefit) the new Q7. At the end of the day, it is a refresh of the old body style, and the A6 under-pinning. Audi has the resources -- financial and engineering -- to make the Q8 a reality. The Model X will be the driving force by taking some small share from a very profitable Audi CUV.
Currently, the Audi Q8 is merely a concept. Because of Audi's engineering, testing, service and attention to detail, I would love to see it become a reality. Unfortunately, for me it is too far into the future.