I know it probably wouldn't be balanced, and technically unneeded because you can just summon void fuel and void water and put them in a boiler, but I think it would be really neat if you could directly summon 165c and 500c Steam.
And while I'm at it with weird suggestions, a way to directly summon heat/electricity from the void. Maybe a void heat pump or something.
More ridiculous : Ability to summon fusion plasma. Because why not?
