It's possible that, like with Intel and their 10nm node, Nvidia will have trouble getting high clocks. It might be one of the reasons why they haven't talked much about it and why they'll, "presumably", focus on power efficiency. This should also mean that they'll be able to add more RT and Tensor cores into the GPU to make them more viable.
We'll probably not see the same jump in performance like with Pascal (vs Maxwell) with their first gen GPUs on 7nm. I fully expect them to just refine Turing. I'll be happy if they manage to get 15-20% by just adding more cores even though they'll prolly not increase the clocks. The increased complexity of Nvidia's GPUs makes the transition more tricky.
Hopefully AMD manages to get something out for the high end market by the end of the year or in early 2020 and TSMC's 7nm+ will not be delayed. AMD needs to introduce ray-tracing together with the 7nm+ node in some shape or form (late 2020 or 2021?). I think Nvidia's 2nd gen RT cores should finally be good enough to get more devs to use this feature (thanks 1st gen beta testers
)