> but does Dell allow you to change your laptop's mainboard for another mainboard with time

Business laptops are swapped out every few years.

Reusable chassis? Literally no one asked for this, it makes no sense outside of a very, very small community of enthusiasts who think it's cool. Restricting yourself to no mechanical changes/improvements in perpetuity is not the flex you think it is.

Keyboards wear out, the chassis gets dented/scratched. Thermal requirements change.

This feature is for no one.