I think that is a very good idea. Especially the changing clothes part. I think there is a mod that does that already (made by corepc if I remember correctly) but it handles it in a completely different way from what your engine would, yours presumably being more efficient. this really isn't a suggestion, more of a question actually. Could this engine possible tell the NPC's when it's raining so they could go inside? Or change their clothes in the middle of the day if the weather takes a turn for the worst? How about just popping inside for a second and putting a hat on when it's rainy?
I've never messed with weather but, browsing thru the functions, it seems I can only know the weather of the current player cell, so most of the [good] ideas you mentioned can be done for NPCs around the player.
Like: player is wandering around the docks, starts raining, NPCs run inside or put a raincoat, or open an umbrella (btw, any links for lower class raincoats, hats or umbrellas resources?)
Also, If the player is outside and it is raining, it would be possible to make NPCs inside the buildings decide not to go out.
I think the problem will be when the player is in an interior cell. There may not be a way to know the outside weather in advance, so NPCs will go out anyway. And if the player goes out and it is raining, NPCs would start running for cover as if the rain has just started.
The fight that takes place every night involving Hauls Ropes Faster may be a good place to test your engine, Simple suggestion, have the fight rake place in doors i the weather is bad.
would it be possible to introduce random bar fights into the Anvil dockside pub?
Good point. Making them fight inside may well be possible.
Since I would have to make those two guys fight anyway, it may not be too much work to expand it to random bar fights.