I bought a used series S off eBay for 200 and just got it to today. Its my first new Xbox in over 10 years. I don't see how something like this could work in a handheld even with recent tech advances. It's relatively small as a console but has a heft I wasn't expecting, and also has a giant exhaust port on the top that's almost half the circumference of the console. Good luck cooling something like that even with a few die shrinks in a handheld format expecting to get anywhere near the same performance as this console.
On a separate note, I hate the Xbox OS cause it's way more confusing than the 360 OSs, but I love the snappiness of the console in terms of performance and speed. I am extremely impressed