Citation for that that launch window for the still unnamed Volta successor?
No Citation, by looking at past release shedules and what AMD does.
Are these your own thoughts or actual and factual information? I'm leaning towards the former. Even though Hynix may have GDDR6 available in Q4 2017 they do need to stockpile it, which won't be completed before Q1 2018.
Thoughts, but it's the most logical in my view. In 28nm last maxwell chip , 980Ti came in Mid 2015. At that time 16nm was starting but apple and mobile makers took first year of 16nm orders and then 1 year later the successor to the 980TI came. With 7nm it's the same and i expect same shedules. 7nm starting in 2018, mobile makers take all at tsmc. I year later Gx104 which will suceed GV102. AMD is aggressively pushing 7nm as posted by their roadmaps. They'll have 7m gpus out in H1 2019 definitely, probably even in early 2019 and you can be sure that nvidia won't just look at them and let them take market share and make money, because of the node advantage. I could imagine Nvidia won't make a full chip lineup with volta, as GM107/GM108 came a bit later, but as i said i don't expect any more of the bigger voltas launching after mid 2018.
Like Micron needed to stockpile GDDR5X with 1080 launch, where no one believed it could be so early? If they write it on their official roadmaps there are good chances, that it'll be possible to launch a product in Q4. Whether they really do it, i don't know, but i wouldn't call it impossible if the chip is ready. Maybe they even launch with GDDR5X, as Micron also has 14Gbps in Q4. Impossible to predict.