I'll let you read the articles from WCCFTech and Fudzilla, but they indicate that the "next gen" cards in 2020, the ones which will replace Vega, are being designed with input from the EPYC team.
So Navi then, would be a Polaris replacement as opposed to a Vega replacement. Is this then the new GPU release cycle for AMD? Mainstream and high end are on different architectures released on staggered years?
Fair point. If they perform at the GTX 1080 level (Where Vega performs in non Vulkan titles) then they will be a more efficient option with identical performance, rendering Vega redundant.
AMD uses "leapfrogging design teams", so it is nothing new that a next generation mid range card performs as well as the previous generation's high end card. Also, you are forgetting that nVidia is well on their way to releasing the GTX 1170 and 1180, which will be a new architecture and will release this year with GDDR6, so it is reasonable to assume that nVidia's mid range cards will also have the performance of a GTX 1080Ti, but since AMD won't have a card on the market until next year, prices are going to remain catastrophically high.
Plus from the buzz going around the next gen Nvidia cards will be way faster than the current gen too.
It's their first new architecture in a long time, so a big performance jump isn't out of the question, AMD experienced the same boost when moving from VLIW4 in the HD 6000 series to GCN in the HD 7000 series, the 7970 is 75% faster than the 6970, so in the grand scheme of things the GTX 1080Ti being mid range performance of the new generation is to be expected.
I have read many place now that the new ones will be 2x as fast. Just scary for AMD when it could be closer to 2 years before we have another mid level option and no high end again. I don't really think it is a necessity for AMD to compete at the very top end. To be honest they don't really sell that many top end cards overall, meaning nobody does. Mainstream is where the money is. However 1440p to 4K gaming is becoming VERY MAINSTREAM. If AMD doesn't have an option and pricing does come back down to sane levels I see a lot of people switching colors in the future. I am sure holding out hope for a surprise from AMD. I absolutely believe competition is best for everyone. I have always loved routing for the underdog! Most interesting to me at this point is the talk of Intel discreet graphic being on the horizon too.
You know I am still really amazed at how well my HD7950 still does. It still is a perfectly capable 1080p card in nearly every game out there. Maybe not at highest levels anymore but still will have you playing. I use mine in my family room on a 49 inch 1080p TV and it is fine.
Whats even more scarier for amd is that Intel as a few new gpu's up its sleeves and one is a gaming gpu..