just like how we can overlay any armor to display over the armor you actualy wear, i'd like to have that for mech bodies, possibly legs and boosters(no arms though). obviously, any mech parts in the cosmetic slots will affect only the appearance. it would give the mech more customization, and you can customize it the way you like, not just pile on random parts to make it better.
Theres already a thread like this posted here: http://community.playstarbound.com/threads/cosmetic-slots-for-mech-parts.133578/
