Going by historical pricing it would be far more tempting to wait for a 1080Ti, or go to the 1070 as a stop gap measure. With the dramatically inflated price for the cards and no way to accurately predict the price, it's a difficult decision to make. £450 for xx80s is tempting, £600+ is a stupid price. I can easily see them launching the 1080Ti at another stupid price of £900.
I can see myself going 1070s in SLI as an upgrade for my 970s in SLI, and then going for a better Volta chip and going for 4K@120Hz. Hopefully Nvidia will address DX12 performance, and 4K@120Hz displays will have come down in price and be a more mature tech. And hopefully competition will get rid of these stupid prices.