My, I can't even begin here. For starters, we're talking about something coming 3 years from now. Today's technology being irrelevant. A system like the switch could have released last month while already being more powerful than a ps4. And no, the gap between the switch and ps4 isn't 3-4x, more like 2-2.25.
Seeing that the A12x in the 2018 IPad Pro is the only chip on the market that even comes close to your claim (and not that close either, it has Xbox One S like performance according to apple) and the cheapest device it‘s in goes for 800$+, what you‘re saying is pretty outlandish.
Also todays technology is extremely relevant to a product coming out 2-3 years from now, seeing that the tegra x1 is a 2015 chip in a 2017 product. And even then it was only really cost effective to use it in the Switch since it was somewhat of a dead end for Nvidia, who pivoted away from gaming applications with the successor chips hard. Nvidia had stock to clear and Nintendo got a good deal.
It‘s fair to assume that Nvidia is working on something more custom and for Nintendos next console, and they’re probably going to make sure that it has the most current architecture, but it‘s not going to be some monster, top of the line chip if they want to have any chance of maintaining a 300$ pricepoint.