I am still working on the new feature that will use sulphur and saltpeter. As you correctly guessed, it will be gunpowder :-)
I don’t know how it will be made to explode exactly yet, what I am working on now is the explosion physics. I want to do a pressure propagation-based simulation that will allow you to do more interesting things than just turn a sphere of rock into a sphere of air and play a “boom” sound.
We’ll see how it will turn out. What I want to achieve is that you will have to be clever how you place the explosives to get the effect you want.