I probably should've clarified, I am talking about x64/Intel/AMD tablets. I agree size/thickness isn't the easiest, but it's more of an engineering challenge than something impossible. I wouldn't mind an undervolted 7 or 10 Watt i5 tablet at all, and currently surface devices are the only "major" brand selling x64 tablets that I know of.
Another interesting thing regarding small/thin x64 motherboards is the existence of 3.5" ultra-small SBCs like those by Aaeon. If they didn't cost so much I'd love to DIY a tiny, thin tablet out of them. The "advantage" of a small motherboard is that you can put it in a tablet, or put it in a laptop with a better cooling system, potentially reducing the need for another new component.
