One issue is that the mobile form factor doesn't lend itself to laptop or desktop class cooling. Some mobile chips can approach the performance of a desktop... until thermal throttling.
There is a reason there are different kinds of cars and trucks for different market segments. Try to build a car-truck and you get the El Camino. Computers are likely going to be subject to similar market forces.
Take a middle/high-end smartphone phone. Install something like Maru OS (but preinstalled and with OEM support). That's it.
I agree with the cooling problems, but a desktop browser and Unix terminal would be enough, and these apps are not that demanding for the CPU.
That's called a tablet. You cal already browse, edit, and ssh from those. When I want a laptop I usually want something way more powerful that can build, run large software apps, run VMs, etc. I regularly max out all eight cores of mine for hours at a time.