Weather effects on the screen - I thought it would be cool if you had water drops / snow flakes show up on your screen during storms / blizzards. Could be an option to turn off for people who don't like extra cosmetics, or crafted goggles so you could see through it. I love the heat shimmer in the deserts and think there could be other effects.

Environmental slot on armor If you're going into a snowy area, you could affix furs to your armor (changing the cosmetic look as well) to get a +cold resist; same for desert / marsh areas with engineering / tinkered water systems / sealant systems, with resists to heat / water respectively.

Just random thoughts.