That was then. This is now. You didn't have the cryptocurrency market driving up GPU prices in 2012 or 2014. The 10XX series is also still selling incredibly well, offers huge performance, there are no real rivals, prices are still high and it's still the performance king. Nvidia and their partners won't want a new card released when prices are still like this:
GTX 670 was released in 2012 GTX 970 was released in 2014 GTX 1070 was released 2016 GTX ???? was released 2018
They released the 1070 and the 1080 at the same time if I remember correctly. However, as founders edition cards I got on the pre-order list last time around and spent £400 I sold that card 4 months ago for £465 because of mining prices. I was also there for the 970 when it was released. In my opinion it feels about right to get an announcement August 20 and if lucky a pre-order list maybe the same day then a release a few weeks after. From my past experiences Nvidia cards have a very stable price and only decrease in value when new cards get released, which causes the tech to drop cause of price/performance. Only anonomy being the mining craze we've had which caused Nvidia to manufacture a load of new cards, which could be the reason behind the push backs.
EVGA warranty service is epic, or at least it was a couple of years ago when I used it. If it's the same now and there's no indication that it's changed, then they will always be my first choice.
Huge difference though between an announcement and release. IF (and its a big IF) they announce Turing on 20 Aug, you're unlikely to see a release until late Sep. Nvidia's CEO said in June it will be a "long time" before next-gen Geforce cards are released. Some commentators are even saying that they won't be released until next year. https://www.rockpapershotgun.com/2018/06/26/nvidia-turing-ampere-graphics-cards-release-date-price-specs/ You're also not seeing retailers drop prices of the 1080 across the board, which doesn't suggest an imminent release of Turing. Also if they are released, they're going to be a sort supply and incredibly expensive as the cryptocurrency market has created an upwards pressure on GPU prices. If you happens you're probably end up with two tier price - the new 1080 replacement at aroud £700 and the existing 1080s for around £400. The new card isn't going to be 60-70% faster than the old one, so buying the new card in 2018 upon release or shortly after release is unlikely to represent good value for money. Prices of the new cards are also likely to remain high throughout 2019.