@ jw0ollard: Well argued. You can set external shader variables through OBGE, so it would be possible to pass weather type and time of day to the shader, and have it do different stuff depending on what those variables were. And I didn't realise you were requesting a new shader for fog, sorry. I suppose that would be possible.
And I would like to see that OVEP list worked on too.

I wasn't
necessarily requesting a brand new fog shader... More simply, I thought the new ray shader could be utilized to enhance the realism of the existing "fog" or the foggy weathers, rather. A way to add a more volumetric feel as I explained would be to make the fog look "spotty" or "patchy" when sunlight is present to cast fog shadows, or "fog godrays". It'd be simple enough to add this effect to the light cast by the ray shader, just a bit of http://en.wikipedia.org/wiki/File%3a%50erlin.png or something more suiting. It could then of course be animated for some added realism.
Although of course ideally, I'd LOVE to have real volumetric fog and volumetric clouds...

I think I mentioned in passing that it would be nice to have volumetric clouds for some nice god rays up in the sky.. Not just god rays cast by objects close to the player. (http://image.com.com/gamespot/images/2007/features/hardware/wic_hardware/wic06.jpg) And if the "fog" encountered in dungeons could be added as a weather effect, plus the god rays through trees and what not, I think that'd make for some awfully moody forests.

Although I have the feeling that that the vanilla volumetric-ish fog shader wouldn't support the god rays at all and would have to be rewritten anyway...
But I'm patient.. I understand that the initial 0.1 version of a god ray shader needs to be released first before things can be added.. Doesn't hurt to throw suggestions out there, though.
Honestly, I think some things are much more important than god rays...
Object/static/architectural shadows are by FAR the #1 thing I miss in Oblivion right now. It pains me to play the game and ask myself why, e.g. a building is lit up even though another building should be putting it entirely in shadow. Or why no objects cast shadows other than PC/NPCs and their equipment.
And of course all the OVEP things that never got to be 100% complete. I was always excited about that stuff.. Also, I request a
rewritten motion blur!!!! And maybe break off the underwater shader into its own mod, with caustics support. Of course, if Ilmryn was working on rewriting the entire Oblivion water system, those could be bundled with that too. =p
Anyway, with access to the depth buffer, the motion blur can depend on the distance from the camera! I hardly like using it now because when I turn really quickly with, say, my hand holding a torch in 1st person, everything gets blurry, including the torch! (Or just exclude any part of the PC during the blur) I understand that's the best they could do back then... But once the depth buffer is 100% sorted (and written into OBGE I assume) what we could do with the graphical mods really takes off!
I should stop spamming the thread for now... I'm just too excited about graphics modifications right now! haha. With this thread and the release of CryEngine 3 I've been doing a lot of geeking out over this stuff.

I wish I could be of help, too, but unfortunately I program in entirely different languages... It was actually always my goal to be a game programmer but now I'm stuck with other kinds of programming.. Best of luck to those working on things right now, especially Scanti with the OBGE work!