Weather effects...

[F1jjYR3]

Adverse weather in the game would be interesting.

It could be set to penalize attacker/defenders/both depending on the situation. Or even degrade individual unit strength unless repaired. 

It would be another level of malus pretty much.

[gamerdruid]

A very interesting idea.  I'm not sure how much new development the 'development team' are actually doing however.  Refining your idea a little, infantry could be affected in a heatwave, vehicles in blizzards or sandstorms and aircraft in volcano ash clouds or solar flares.  As you state, a type of malus but affecting only some of the attack units.  Maybe the same effect could affect the defence teams too.  

[F1jjYR3]

Infantry might be affected by extreme heat/cold equally.

Maybe even armor and air but it's easier to attribute their adverse affects in varying degrees. Air could be less affected by heat for example.

As for defense fixed guns and barriers could be least affected.  

Maybe a malus penalty can be paid by buildings and defenses with a multiplier that reflects how many penalized units you have attacking and defending.