The cantilever design is indeed an elegant solution, though it can make it a little more difficult to hit the top row of keys.

I was thinking that this laptop is kind of like a Pi 400 + battery + screen. If we look at is this way, then what the OP wanted is kind of already available - you can buy portable computer monitors.

Interestingly, the Pi 400 + screen is kind of a "smart" keyboard combined with a "dumb" monitor, while the iPad Pro + Magic Keyboard is a kind of "dumb" keyboard combined with a "smart" monitor. It seems like both approaches have advantages and disadvantages.

Not exactly what you're talking about, but I've seen a few RaspberryPi + iPad + External Keyboard setups where they either use the iPad as an external display or VNC into the Pi from the iPad. IIRC you can power the Pi via USB C -> PoE on iPads with sensible ports on them, so you don't need an external battery or UPS.

Again, not what you actually want (I share your pain/longing), but damn if it isn't starting to get close.

Honestly this is my dream as well. The iPad Pro has a gorgeous 120Hz Display, the most powerful ultra mobile CPU and is incredibly light. I have hidden hopes that Asahi Linux will offer a path if a new exploit is discovered.