Hi! Thanks for playing!
All of the cars and tracks from the three Rush games are planned to be added. Car paint is coming in the 0.11 update which is right around the corner! I plan to enhance vehicle customization further than the original games ever did, but I don't have these features penciled into the dev roadmap just yet so I can't say how soon they will be added.
The community voted between online or split-screen multiplayer a while back with online being substantially more popular, so online multiplayer will be added before split-screen, but I still plan to add that eventually. Rush is a great couch co-op game and game modes like Battle work especially well with it! (Be sure to join the Team Rush Discord server to participate in community votes!)
I don't have plans to create a replay feature before the 1.0 release because this would take quite a bit of time away from more important features, but I could see it working well within the game so I will add that to my notes to add after the 1.0 release in the future. I had not considered a photo mode previously but that would be easy to implement and would suit the game quite well so I'll look into it!
Thanks for the suggestions and feedback. I hope you enjoy 0.11 when it launches!