I dont think Rewind will get added to multiplayer.
Think about it. For your car to be "timewarped" back to a good spot, it would surely mean all the other players would also be "timewarped" back to a certain spot. If however, it only affected the one guy who was doing it, it still would not work. I could only imagine it rewinding you back to a spot, only for it to put you on the racing line resulting in your car being smashed into. I seriously doubt Turn 10 would be so stupid to put the rewind feature in Multiplayer.
I may be wrong though, although i hope i am not.