Sorry for the rant, but as an auto engineer who sees the inner workings of what it takes to bring a car to production, the chances of this happening are zero. The cost to develop a mostly new car are astonomical and Nissan simply doesn't have the sales volumes to justify it. We will be lucky to get a mildly reworked Z34 with a refreshed skin and a modified powertrain from an Infiniti product. Nissan sells less than 10,000 Z cars per year when the product is fresh and is selling around 3,000 per year near the end of the product cycle. There simply aren't enough sales to ever repay the R&D and the tooling. An all-new Z35 would cost upwards of a billion dollars. Even if they could sell 100,000 cars over the life of the product, that's $10,000 per car just to pay for the development costs. That doesn't include the manufacturing costs, raw materials, supplier parts, marketing, or profit. Even at $50,000 MSRP, they wouldn't be able to justify it. Now, reuse the chassis, most of the body, and rework an Infiniti engine and that figure might drop to 200 million dollars. Now, only $2,000 per car goes to pay for the R&D and they have a much better shot at success.
There is a very good reason that even Toyota, the leader in cash on hand, didn't develop their own Supra or FRS. It simply doesn't pay off. Even when the Supra is 90% BMW, it will still go down as a poor financial decision for them and the next time around, they might shy away.
The C8 Corvette is interesting because the R&D costs were huge, yet GM spent the cash to do it. Volume is their friend and they will sell 50,000+ C8's per year. GM is also likely to axe the Camaro again which freed up money to do the C8. There will always be old guys with cash that just have to have a Corvette as a 3rd car. There simply aren't enough young people with money to justify an all-new Z.
I just hope Nissan does enough with the Z34 refresh that sales will be in the 10,000/year range again.