So the Series consoles have been on the market a bit over a year now. According to the VGChartz charts tool, the Series consoles are sitting at 6.14 million consoles in North America, 3.65 million in Europe, and 0.13 million in Japan. If we assume another 8 year console cycle, and one of those years is out of the way, and we also assume the Series consoles sell at roughly the same clip that they are now, that would put the Series consoles at around 43 million North America, 25 million EU, and 900k Japan.
Those numbers will fluctuate of course. I think 900k in Japan would be extremely optimistic, and 25 million in Europe again would be a tall task. But 43 sounds about right for North America. My predictions
Rest of world: 12 million (I am assuming about double what the Xbox one did for this category)
Total: 77.5. Which is more or less my original 80 million guess. I think this is doable