Truthfully, I have nothing against having a 24 Hour cycle which obviously means nighttime. While I personally wouldn't use it all that much unless in a race that mandated a night time race start, I do think having a 24 hour cycle could allow for some very beautiful dawn/dusk views. Rain, however, I seriously don't care about in the least and if it were up to me I would have the dev team spend their time focusing on other areas of the sim.
It is so freakin' hard to accurately simulate driving a car on dry pavement. While those of us here are happy with Kunos's attempt to simulate driving on a dry surface, I think we would all agree that there are still so many flaws in the physics of AC. Maybe a few less than other sim, but let's not kid ourselves, we just don't have the processing power to truly have a 99.9% accurate driving/racing simulator. And that's okay! We don't need 99.9% accuracy to have a driving sim that satisfies people in their fantasy to be driving in their living rooms and spare bedrooms.
Now, add rain to the mix. Add standing water and how puddles, no matter the size have an effect on the physics of the car's movement. Program in the intricacies of a car's tread pattern moving that rain water away so the tires can provide better grip. And on and on and on. I don't believe simulating rain is worthwhile because I don't think it'll end up being anything like real rain/driving in the rain.
I know I'm supposed to suspend disbelief since I'm playing a "video game" in the first place. Well, I can't completely suspend disbelief. Not 100%. Who knows? Maybe I'm wrong and there have been some algorithms that can simulate rain & driving on a wet surface brewing in the minds of Kunos developers. I would love to be proved wrong. There are just some things that are easier to accomplish with today's technology and I'd rather Kunos focus on those things. Unfortunately, you need that marketing gimmick if you're going to try to command a good slice of the PC sim racing world in 2018.