According to all the screenshots that were released, I don't think neon will be included. They have neon in MC3 because it was all night race. As soon as they add the day-night cycle to MC:LA, it's just lame to see neon light up during the day time.
There will be neon. http://i37.tinypic.com/2ewmtz5.png Second column, about half way down. "While it's not in the title, DUB magazine is still onboard to provide guidance on car customization features, which exceed even the options in Midnight Club 3. From scissor doors to UNDERCAR NEON IN THE COLOR OF YOUR CHOICE, you can craft cars that are literally one of a kind with kits, rims, and parts from most of the major manufacturers." (Credits to Game Informer for the article and krazykubano for scanning the page and posting it in the 360 version of this board)