How long until a ps4 level $400 hybrid is possible?

[captain carot]

What are people talking about here?

x86 and full compatibility? Won't happen to soon.

ARM with a comparably strong GPU? Might be not that far away.

PS4 power in docked mode? Again, that should be available in a not so far away future.

PS4 power while in mobile mode? There is a reason, actually multiple reasons, Switch clocks down. The same would apply for every other handheld.
Battery life, not only in terms of how long one charge lasts but the overall lifetime.
Cooling/getting rid of the heat. Switch actually has a built in fan. But the more power, the hotter it get's.
Cost. We are talking about SoC, RAM, FLASH-memory...

Yes, there are those nice things like die-shrinks. But a new node isn't always what it seems to be. Companies started 'cheating' about transistor- and gate sizes and other stuff some time ago. Two different 14nm manufacturing processes might be incomparable today. And new manufacturing steps don't always bring the expected results in cutting costs and improving energy efficiency.
Finally, new shrinks take longer and longer the closer we get to the limits. Not to talk about stuff like bus width and other 'little details'.

Tegra Xavier right now is intended for AI systems, deep learning, self driving cars and stuff like that. Mainly because you make more money there than with a gaming device or tablet and Xavier is relatively expensive in the beginning.

A Xavier device should come relatively close to PS4 power levels, at least in docked mode and would be possible to built very soon. But not at the 400,-$/€ pricepoint.