Dan's reasoning for no night/weather in Forza 4:
“For Forza 4, the majority of our graphical investment went into our new image-based lighting (IBL) model, as well as new material shaders, which give our cars and tracks such a realistic, detailed look. With IBL, supporting the general look of night is not particularly hard.”
“However, we take frame rate pretty seriously—we believe that having a solid 60 frames per second (FPS) experience with no tearing is very important for a simulation racing game.
Delivering night is about more than just getting the general look right. As we found on the original Forza Motorsport, having multiple headlight projections with multiple cast shadows is computationally heavy—even using clever tricks like we did on the less powerful original Xbox platform. This makes delivering a strong night racing experience very difficult at 60 FPS without significant compromise.”
“Creating believable weather effects also depends upon gobs of particles and lots of shiny, reflective surfaces. There are several tricks for doing this, but it would still have made delivering the new graphical fidelity of FM4 at a solid 60 FPS nearly impossible in our development timeframe.”
He mentions that they could have done something to include weather and other effects.
“If we cut down on the number of cars on track, used original Xbox-generation car models, dropped to 30 FPS, or (and this would be the most effective solution) built specific tracks from the ground-up to have less detail and thus extra performance headroom, then night racing and/or weather conditions may have been possible.”
Read more at
http://gamingbolt.com/forza-4-does-not-include-weather-effect-or-night-racing#fJh5S1xHdwBg32B5.99
Dan's reasoning for no night/weather in Forza 5:
The cheapest track Turn 10 built for
Forza Motorsport 5 took nine months. It was an updated version of an older track, with heavy modifications to bring it up to the team's next generation standards. "Everything had to be rebuilt," Turn 10 creative director Dan Greenawalt told IGN.
Courses the developer built from scratch with entirely new assets -- whether for the sake of looking better or achieving better accuracy -- took considerably longer. This is why we haven't seen nighttime racing or weather effects in Forza 5. It's why we may not get to for a while, if ever.
When we do things, we do it all the way.
Adding night and weather to an existing course "is not a minor thing, it is not a 'add a little bit of time, throw it in' thing," Greenawalt said. "When we do things, we do it all the way. That means physics, that means changing conditions, that means everything. So that is not the sort of thing that is easily undertaken in a patch.”
So, what about building a new course around rain and darkness? Greenawalt explains, “To build a new track that would work at night and in wet would mean a bespoke track. Everything we build is bespoke." To start from the bottom up means at least another nine months of development -- that's just to get the course up and running, never mind modifying it with new water and car physics, and new lighting.
"If we wanted to make one of those tracks work with the added particles or projected shadows, and of course adding the physics to do something like night and wet, it means re-engaging those tracks. I’m not trying to give an excuse, I’m trying to give context as to why this is an order of magnitude higher than something like
Drag and Tag, and other things we’re looking at from the community.”
Greenawalt explained that "it’s fair that people ask for the features they want, and we’re here to make fans happy." He knows that both night racing and weather are staples of the genre. "It’s not where we chose to put our investment in Forza Motorsport 5. We chose to be 1080p and 60 frames per-second, and have that solid performance.”
To that end, "we’re going to try to make the best decisions we can to get people to really, really love the game.” Those who don't may find their feedback considered for future updates to Forza 5, as always.
. I wouldn't expect it until F7, the tech maybe to immature yet i'd rather they use those resources improving other aspects for F6.
There were other reasons to.