Prediction: Sony will have a portable that will play PS4/5 games

[Soundwave]

PS4's chip even at 7nm would consume way too much electricity to be feasible in a reasonably sized portable.

You're likely looking at 30 watts still just for the chip.

Playstation 5 portable is a laughable proposition unless Sony is cutting off their knees and making a system that's basically a PS4 Pro redressed, in which case, Microsoft will be able to exploit such a weak new console and take over the home console market. Simply cutting the resolution by 4x only saves you so much.

Sony could make a custom chip portable with PS4 tier visuals by around 2020-2021, but it would require PS4 games to be ported from scratch to a new architecture  ... and Nintendo could very easily counter that with a Tegra X3 based Switch which would be compatible with (by then) hundreds of Switch games and Sony is back in a bad position.

Sony has routed Nintendo out of the dedicated home console space, they can enjoy the fruits of that, but portables are likely always going to be difficult for them, moreso now because Nintendo's majority/entire focus is one basically the Switch ... Sony will never be willing to make that level of commitment to a portable platform. Is Sony willing to put Uncharted 6 as a Sony PSP3 (or whatever) exclusive? Not a spin-off but the actual next game? I doubt it. Nintendo is willing to put major IP installments on their portables, Sony has never been willing to go that far.