This week I've been working on "textured painting" for my Mesh Paint tool. Basically you can use object material/texture to define paint color and strength.
This works on both solid and volumetric materials. Texturing can be used to add some randomness to paint coverage or even better: to allow painting with smoke! You could make dirt clouds that affect environment etc.
Here's a short demo of smoke domain being used as textured "Paint" object. Painting with smoke: