sometimes ago i've started a topic for "feature requests", one of the most voted is physical sky with clouds.
i want to link here all the paper and opensource software that could interest devs or any other volounters for adding this feature into Luxrender.
Volumetric 3D clouds renderer
papers & web pages:
http://www.vterrain.org/Atmosphere/ at the site... the linked paper is missing but this could be the missing one.
title Real-Time Rendering of Planets with Atmospheres
Real-Time Cloud Rendering
Lord Crc also suggested
.... perhaps we could make a script to generate scenes which could be rendered with lux, which would generate skyboxes (using env cam), that way one can do an overnight, get a nice skybox and use it for several scenes, we already have a cloud density volume, so...