It would be cool if the bottoms of MacBooks weren’t flat and instead wavy or rippling to increase surface area. There are probably a lot of cool designs (ayyyyy) you could machine in.
Is there a value to increasing surface area on the top or bottom case of a MacBook? I'd imagine most of the thermal management is achieved by fan-directed airflow through the internal heatsinks and convection through the keyboard.
There are laptops like that (e.g. the fanless Lenovo Chromebook Plus 14). No idea if it was actually engineered like that for thermal reasons.