I'm thinking maybe a new ip series is good. They should take some inspirations from older Need for Speed games. A mixture of Underground and Hot Pursuit (They were the best part of the series ).
I like the police chases in Hot Pursuit, but I also love the Underground open world and customization.
Features that need to come back (From what I think)
Hot Pursuit (series): I like to play as both cops and racers, it's an interesting mix
Underground (series): Bring back customization! It's a great feature and Underground was like the another source of Midnight Club.
Most Wanted (2012): A lot of songs in the game (had a pretty big soundtrack list), I think they should bring a mix of EDM, Rock, Rap, etc.
Prostreet: Now, I know I shouldn't really bring this game up, but I do like to have some type of dirt spec car in the game with the drag races. I do like drag racers they are interesting.
Hot Pursuit (2010): It would be a great mixture of a realistic-arcade type game, I think this is what made this game interesting.
Rivals: I do love the weather effects in the game, but want needs to be removed is the Autolog. Also, if I want to play single player. Why wouldn't the main menu actually pause? For me, this was problem since if I had to stop to do something else while finishing the game it would still continue the pursuit.
Others: I think a mixture and balance with Japanese, Europeans, and American cars would be great as a lot of these racing games are lacking Japanese cars a lot. Personally, Japanese care aren't my favorite types of cars, but a balance of all 3 would be great for others.
I think a Underground Reboot is great, but then again it would be better to have a newer Ip in the series.