Can probably take an educated stab at what the new volumetric fog will entail. Can look forward to animated fog with density control, quite probably individual fog volumes (actors) with controllable parameters if not at launch then at some point after it, volumetric fog being affected by any and all direct lights and shadow casting lights, and pretty decent performance. Using it for clouds is entirely possible, though may not make launch/have to wait for a community effort.
A fairly fast, robust, and stable way of doing volumetric shading coalesced in the games industry around last year. And while Epic might experiment some, a lot of it is robust and universal and so not going to hold a lot of surprises. The good news is of course that it’s quite flexible and fairly fast, can probably extend to other types of particles such as smoke with some effort, and can even receive indirect lighting (depending on how Epic ends up doing that).