The more I think about it the more I agree with
@Raccoon and hope they've really put effort into making it PORTABLE. Keeping it THIN. My handbag JUST ABOUT fits an OLED Model. Next gen is already going to be a stretch, but if they make it big bulky and heavy for the sake of performance for the sake of a handful of extra games not having to put in as much optimisation, that will be a BAD decision. Nintendo's bread and butter is HANDHELD. Hand. Held. Small enough to be held in hands without fatigue, even for children, small enough to be taken anywhere, on a plane, on a bus, on a train. Small enough to fit in a handbag, a satchel, a glovebox. If people want a ridiculous gaming device on the go that basically requires wall power, get a Series S and an xScreen or a gaming laptop. Nintendo does and in all likelihood will continue to make HANDHELDS.
And there's nothing to suggest they won't! T239 on 4N, which still seems to be the most likely scenario, has power consumption no worse, and so heat dissipation no more dire, than the original Nintendo Switch. With the improvements we've seen in battery density and Nintendo's own improved motherboard design since 2017, even at the same power consumption we could see a device that has much better battery life, but that ISN'T ANY THICKER. Nintendo wants this to be successful, so they want it to be appealing, and that means visuals and comfort. Thinness is an obvious target the needs of which are met by T239.