A 1080 would not be enough to provide a generational leap in visual fidelity over current gen games. Especially when all games are going to be 4K across the board. Not even close. One X already performs close to or better than the 1070 in some games.
We will most likely be looking at checkerboarding with better quality than Horizon Zero Dawn had, which is fine by me.
If they managed that with 4.2TFlops, then 10TFlops allow for a decent jump in graphics as well.
The main upgrade this time, will be the CPU.
This changes game development on both consoles and PC gaming, greatly improved AI, physics and audio.
They can have a more efficient architecture by next year that can give significantly better performance at the same or less TDP.
I believe their next GPU architecture is going to be along the lines of Vega, a graphics card that also does a lot of compute for enterprise.
While it might perform well at gaming, it won't be the absolute best that it could have been.
The next arch is named Arcturus and is expected in late 2020 or mid-2021.
This Architecture is a completely different architecture due to leaving GCN behind, meaning their software is probably not going to be stable enough for a console in the early months of release. (in my opinion.)
Which would then mean we would probably have to wait until H2/2021 or H2/2022 for a console with the new architecture.