We will probably still have cases that do not fit well into this system. Some situations will exist where a prediction key exchange is not feasible. For example, an ability where any one that player collides with/touches receives a GameplayEffect that slows them and their material blue. Since we can't send Server RPCs every time this happens (and the server couldn't necessarily handle the message at its point in the simulation), there is no way to correlate the gameplay effect side effects between client and server.