The main issue with this is the type of fractals available for clouds, blender just lacks good fractals designed for clouds.
Terragen is one of the best in reference for cloud fractals, I can get nice ones with Lightwave and it´s fractals, especially dpont´s Rman shaders featuring gardner clouds and weather and much more.
Ultimate sky however, apart from the lack of proper textures for clouds, it seems to be none full volumetrics, somekind of hack with poor edge softening and lack of depth in clouds optimized more to be fast than realistic it seems.
someone posted a shader/scenefile over here with a volumetric box and some noise nodes embedded in to a master control node, it was quite nice, but suffers from some artifacts, and due to all the noise fractals needed, it becomes too slow…it needs one or two good fractals in One node, not 10-20 nodes slowing down the render when the node system have to parse it all.
Using volume boxes and noise field will not give you infinite cloud layers like vue or terragen though, someone have to write volumetric handler for that, or you have to fake with placing cubes out in distance, and perhaps compositing.
Same goes for vdb imported clouds, you can´t really get that working for full infinite layering either.
Vue and terragen clouds, vue can be semi decent at times, but it´s cloud fractals are based on fractals not designed for clouds, unlike Terragen, thus many of the vue clouds are blobby and not really so realistic, with some exceptions for those artist who can push the fractals the most.