The game has come so far and it has the tools in place to become even greater.
The weather on Planets is great! However, solo and even group Survival play have only NPC enemies to keep the challenge. The Weather system and the recent Water mod have proven that the system is robust enough to add more environmental challenges.
Note that I've tried to NOT add new blocks if possible to keep the effort as low as possible.
1) Blistering heat or cold. Heat on planets (there are some lava worlds on the Workshop) that can cause injury or damage blocks and cold that can do the same. Pressurized areas are warm to prevent cold damage and Heavy Armor Blocks can resist heat.
2) Radiation. This will mostly injure the Engineer. It should be resisted with Heavy Armor Blocks.
3) Dust storms. This is mostly for space since we have sandstorms on planets. Dust traveling at high velocity in space can damage components and scour a hull. Flying through it at high speeds makes it worse.
4) Toxic or caustic environments. Even in a habitable world or in a pressurized area there can still be toxic or caustic substances. Toxic ones would injure an unprotected (visor up) Engineer. Caustic ones would injure both the Engineer and exposed equipment.
In some cases (like radiation or caustic environments) perhaps a new type of suit would be protective enough. Such a suit would require components to make.