Client-side prediction can be hard to add to a existing codebase. Adding it to a game and not breaking backwards compatibility with user-made content and script

Client-side prediction can be hard to add to a existing codebase. Adding it to a game and not breaking backwards compatibility with user-made content and scripting is going to be impossible. Remember: real people have spent real money on in-game items, you can't just rev the API and say the old items are gone. You can't do refunds either: players paid other players for items, ten years ago, using long-expired credit cards, sometimes from expired people.