agreed. I do upgrade parts of my laptops, but it's just like buying extra batteries and sd for my phones.

What you could do is to try to define a standard form factor for a range of mobile mother cards and screens, a produce bodies that can accomodate them.
This way you could have some kind of customization, and you could change the MB/screen from time to time, or the body (w/ w/o hwk, extra space for battery, etc..)

But I think there is no way you can change the main component of the MB (CPU, GPU, ram and any other chip) without loosing lots of space and efficiency.

Maybe some king of micro PCIe could be added to the MB too, so you could add compass/gps or fancy things like that, that have small impact on tdp/volume.