There is actually a lot of people that want to buy a card somewhere between the 1060 and the 1070 because the 1060 isn't enough of an upgrade and the 1070 is £360+.
Indeed, and if you look at the gap in Cuda cores from the 1060 6GB at 1280, to the GTX 1070 with 1920, that's 50% more, which is the single biggest gap in the entire Geforce line up. The gap from 1050 -> 1050 Ti is 148 cores (20% more), the 1060 3GB to 6gb is 128 cores (11.1% more), GTX 1070 to GTX 1080 is 640 cores (33.3% more) and being addressed now with the GTX 1070 Ti, and finally the GTX 1080 to GTX 1080 Ti is 1024 more cores (40% more).
I'll get my coat though, as apparently it's complete rubbish and I know nothing, even though I labelled it as speculation.