Stefano basically confirmed any AC2 would have night and rain. It is in the "what engine does AC use" Thread in chit chat area on AC forum. An interesting read.
I was going to mention that thread from the official forums...A couple of tidbits that fit into the current conversation here - All answers are from Stefano, of course:
Q: If you were to start developing a sim now would you go for any of the available graphic engines? Does it make enough commercial sense to not have to develop/update your own?
A: I would surely spend the initial part of the project evaluating what's out there, including 3rd party engines.
(This is not really a question, but Stefano responded)
Q: If I remember right, in one of Stefano's "Look What The Cat Hacked In" live stream, He mentioned that rain is possible but it need a lot of calculations around physics and so on. So a lot more CPU, RAM,...
A: not really, no. Physics would be the easiest part of the lot considering it's already "baked in" the tyre model.
(Again, not really a question, but Stefano responded)
Q: I always understood that the single light source was a design decision (and no problem really, to me at least) but I've been curious, given that NKPro had rain, that it never was a consideration for AC. Of course now hearing that AC is itself not an evolution of NKP it makes more sense.
A: the story about the 1 light source was pretty much like this:
- AC engine started its life as a "deferred" graphic engine, which is a style of rendering that makes it trivial and performant to add light sources
- Some months into the development I started to look into AA and with DX10 as minimum hardware as target MSAA+deferred=impossible
- One day I wrote a "Forward" (as in traditional rendering technique) engine with MSAA that looked much better and was also faster. So with Marco we had to decide between crippling the engine performance (and loose MSAA+soft transparency) to support an exception as night racing or optimize for the 99% usage and get better AA limiting ourself to a 6 to 6 cycle. We went for the 2nd option.
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Obviously if we ever see an Assetto Corsa II it will have to have 24 hour cycle & rain because that's what people scream for the most. You know how someone gave us the breakdown of how many people actually go online in AC - it was something shocking like 13%. I could be way off with that, but it was a shockingly low percentage. I have a feeling that the usage of rain will be even lower. I know just about everyone is going to say, "No way...I'll definitely be using it all the time!" I'll believe it when I see it. But, I know that's not the point. You've got to be able to compete with "features", so it's just a necessary feature that must go into AC2.
I don't know if the Unreal Engine is the best way to go or not. I will say that I was mighty impressed by what Ian Bell was saying a few nights back on this forum. If PCars 2 can accomplish the things he says it will, AC is going to have a lot of work ahead of them, if they want to keep up. If I'm not mistaken, I believe Ian Bell answered a question about FFB with an answer along the lines of, "We have 10 programmers working on FFB right now..." 10?! Clearly they have resources, so I do believe that PCars 2 will be pushing every drop of performance out of the game engine.
Maybe I'm not remembering things clearly, but I think if you use the Unreal engine you have to give 5% of your sales to the makers of Unreal Engine 4. A friend who works in game development (not sim racing) told me something like that fairly recently...definitely within the last 6 mos to a year.