We're kinda there already. Most recent laptops I've seen have a tiny motherboard not even taking up the whole width of the device. Under the keyboard there's usually the battery.
Don't forget a significant part of the weight has to be towards the front edge so you can tilt the screen back without flipping the whole laptop. Some of my cheaper atom based laptops (with tiny motherboard and batteries) even have a metal bar in there for that purpose.
Right, but my idea was to do something like shove the mainboard up into the bezel above the keyboard and battery into the palm rest, with nothing sitting under the keyboard except maybe ribbon cables. That’d get you a laptop with a thickness of under an inch that still has a keyboard that’s not compromised and keeps weight shifted to the front. It’d simplify repairs to some degree too since there’d be very little stacking.