I don't see how that's possible when the Ally X has the largest battery in a handheld to date, by a very large margin, and it's already on the heavier side (it weighs noticeably more than the much larger Steam Deck OLED). Battery size is also directly tied to weight, so going from 80Wh to 150Wh will double the weight of the device almost.
Again, show me a laptop with a 150Wh battery to start out,
this is what a device with a 300Wh battery looks like and it's about the size of 4 Ally X's, coincidentally.