It was missing in Forza 2, 3, 4 and 5.  Although I have no idea why 5 didn't have at least nighttime racing since all the cars have fully working headlights (well all the cars that have headlights there are some open wheel cars that don't have headlights).

Ahhh, so it's more like a "return" of features. I get it. Well, I'm glad to hear Forza fans are getting it. Seems weird that it wasn't there all this time. There has to be a logical reason for it.

1080px suggests horizontal is not 1920

Well they didn't wanted to add it because it would have slowed down the frame rate.  I can see that being the case with the rain but nighttime racing really isn't that much more demanding than daytime racing.  Nighttime racing really should have been in all regular Forza games.  Also I'm pretty sure that the cars in the second game are based on the cars from the first game so adding working headlights and night racing wouldn't have been much more work.

Because go-ju and roku-ju totally sound the same, right?

Well its already been confirmed that it was a typo its not the only one since they also misspelled Daytona.

Please bring Maple Valley back! I loved racing on that track in Forza 4.

I know, but the error is clearly a typo or English to Japanese vocal mistranslation. Japanese to English isn't really a possibility. No Japanese would confuse 50 for 60 and even non Japanese with the most basic grasp of the language would not think roku-ju was go-ju, where as the phonetics on "fifty" and "sixty" are very similar for Japanese listening to american English, so its likely that the mistranslation occurred over the phone or Skype call

Highly doubt it but it looks like a improved version of the Rio track from the first game will be back I want most of the remaining unknown tracks to be real life racing tracks since going by the third pick they will add a lot more race cars to the game.  Plus Fujimi Kaido trumps Maple Valley even though I suck at drifiting if they bring back any other fantasy track from previous games I would want it to either be Fujimi Kaido or the long version of Rally di Positano from Forza 3.  I'm hoping that some of the real tracks they will bring back are Mugello circuit, Twin Ring Motegi, Suzyka Circuit or Tsukuba Circuit.

Doesn't "px" mean pixels as well?