What we may see in a next gen console depends on various things such as the cost of using it in a console as well as things such as the power and heat constraints, I don't expect them to use the highest end GPU hardware available as it will probably be quite costly to use and not feasible for a console due to things such as the previously mentioned power, heat and cost constraints.
I'm hoping their GPUs are capable of 16 or above TFs if they're releasing in 2019 and on wards, however I don't know how plausible that is. I think that them having GPUs that are capable of at-least 10-12TFs is quite plausible but of-course we don't know for certain. IMO that kind of increase seems a little low though coming from mid gen machines so ideally I'm hoping for 16 or above TFs with 24GB or more memory, I think somewhere between 12 and 16 TFs is quite likely though.
If their flops are comparable to Polaris, a PS5 with a 16 TF GPU would be a huge upgrade from the base PS4 as it would be theoretically over 8.5x faster, a PS5 with a 10-12 TF GPU also still be a sizable upgrade as the GPU is theoretically around 5.4-6.5x more powerful but as I said before this kind of increase seems a little low IMO.
Fortunately the CPU and memory the new consoles will have are huge factors which contribute to the power and capabilities of the machines as the GPU power doesn't necessarily tell the whole story, although it is very important. So in the event that the new consoles launch with GPUs that are a bit lacking they'll hopefully be huge improvements to their CPUs and memory systems. With faster CPUs and more memory you can create larger worlds which are more advanced and more detailed on a simulation level among other things!
EDIT:
After thinking about this more I think a console with a 12-16TF GPU is the most plausible outcome for a 2019 next generation console launch, above 16TFs may just be wishful thinking on my part but it will be interesting to see how GPU technology develops over the years and what tech becomes available for PCs and Consoles. There could be some really nice architectural improvements from newer GPU technology in 2019 and onwards.
Regardless of the mid gen consoles, a next gen console with a significantly faster CPU, 24+ GB of memory and a 12TF GPU would be a huge upgrade from the base PS4 and Xbox One. A lot more can be done with games on hardware like this as they'll be unshackled from the limitations of the base PS4 and Xbox One consoles outside of cross gen games.
