So I was in the middle of making a ball-shaped smoke, but the volumetric effect didn't work following the basic shape. It remains cube in Eevee Blender 2.8; while in Cycle it works, but in Cycle it takes thousands of years for Render.
Eevee's support for volumetrics is quite limited.
From the blender manual:
Eevee’s goal is to be an interactive render engine. Some features may not be there yet or may be impossible to implement into Eevee’s architecture without compromising performance.
Read: Eevee Render Limitations
Object volume shaders will affect the whole bounding box of the object. The shape of the volume must be adjusted using procedural texturing inside the shader.
What that means is that the volumetric shader will always be a cube or a cuboid.
As far as I know it is meant more for haze and atmospheric effects, so volume would be used on volumetric domains, not so much in detailed meshes made of smoke or dust.
Maybe someone that actually cares for Eevee can clarify.
Here is the solution that works with Emission Shader, Principled Volume and Volume Scatter.
You can try the spherical mode of the Gradient Texture. I am still experimenting and I want to make it transparent in the middle, but I can't work it out yet. And for more interesting results, maybe try to multiply the Gradient Texture with the noise and play around with the texture coordinates. This is specific for Spheres only !