This suggestion addresses how some people like the current temperature advantages or how some people want a different setting on their “favorite” armor. So here’s a suggestion to address the issue:
a. Strip all temperature advantages from armor sets (armor sets = 0 advantage (neither hot nor cold))
b. Base all advantages on the type of lining used in the construction of the armor type:
(1) Cold linings such as a fur light armor lining, or fur medium armor lining, or fur heavy armor lining gain cold protection (keeps the wearer warmer)
(2) Heat linings such as reptilian hide light armor lining, or reptilian hide medium armor lining, or reptilian hide heavy armor lining gain heat protection (keeps the wearer cooler)
Thus, something like Silent Legion armor (which seems to be many people’s favorite) could have either cold or heat protection based on the type of lining used in its construction.
As far as the art department would be concerned, the same armor models can be used for either set on the wearer (no changes needed). For icons in armor construction, at most, maybe do a recolor for one set of the linings (maybe a tan or light brown for heat linings and keep the existing gray linings for cold).
As a result, armor sets would increase in versatility (players can ‘wear what they like’ regardless of the biome they are based) and greater player customization in their fashion choices.