Hello,
I think that thermodynamics engine can be a good way to produce mechanical power, it need to introduce temperature in lava, water, snow, ice. The temperature also can be use to force player to wear armor to protect from the cold and if it is too hot, the layer can be handicap.
This idea is in the way of season in minecraft that will be implement.
Tyrion78
PS : I am sorry about my poor english level (I am french).