Just as it says, what you guys think? Adjusting haze and fog height after image is rendered? Density too, and anything else. 
now, could someone make it happen? :evilgrin:
You can do that with existing nodes. See http://bebraw.googlepages.com/volfog.png and http://bebraw.googlepages.com/volumetricfog.blend .
The approach may not work in all possible cases and the example could be probably better but tweaking it better is left as an exercise for the reader.
sweet, thanks! Still, wouldn’t it be nice to have one anyway?
well, fog is usually an above-ground-to-a-certain-height kind of a thing, and the compositor has no knowledge of that. It can get distance away from camera via Z info, which you can use for mist/focus.
could it be baked like ambient occlusion? and then placed into the compositor?
The best thing to do is just render LQ versions and tweak the fog until it is what you want. In theory anything could be done, implementing it can be hard though, and something like this could take lots of processing power
Yes, it would. Think of Photoshop’s layer effects. Sure, you can duplicate layer effects with Photoshop’s regular tools. Layer Effects aren’t there because you can’t get them any other way, they’re there to save time. Why take 100 steps when one will do?