That’s a laptop from 2 years ago; the new M1 MacBooks are more indicative of where things are headed in the future. Things like memory and any custom ICs are just going to be integrated on the same silicon as the CPU in most cases.
Still bigger than a smartphone (it occupies the entire width of the laptop (when counting the heatsink, 2/3 of the width otherwise), and around one quarter of the whole area).
Also, your original sentence was
> Modern laptop motherboards can easily be about the size of a cell phone.
Here we see that the one and only best laptop in this regard comes close to the cell-phone-sized motherboard. That's far from what “modern laptop can easily be” means. Most laptops sold today have a much bigger motherboard than this.
(BTW, as much as I'd like to see non x86 laptops going mainstream, software compatibility is huge issue for an ecosystem as diverse as the Windows one (and Roseta 2 being too much of a coinflip isn't encouraging…), we might get there at some point, put it's gonna be slow and painful.)
