Doing anything where mispredictions result in a few frames of doing the wrong thing escape to the user is going to make games feel really inconsistent. If the game is running at 60fps and you have a system that can predict with 99% accuracy (which seems wildly optimistic) you’re still going to have mispredictions at a pretty high rate.

Not to mention that the game will have to be written especially to allow for the simulation to be rolled back and forth. For example a misprediction triggers a sword swing it turns out you didn’t make that traps the player in a state for a second. You end up giving the player a horrible experience where the game seemingly has a mind of its own. Or you can roll back and interpolate from the bad state back to a good one which would be ideal. Then the middle ground is to rollback and have a cut in the action back from misprediction. Then you realise this is happening every second or two.

Game state prediction doesn't cut it, or rather there's no point to it. The rendering is done server-side - remember they're streaming HD AAA games to televisions and tablets. There's always going to be a round trip between pushing a button and something happening onscreen. Google did say something about device inputs being sent straight from the controller to the server. Maybe this means they will cut down on latency between the input and the server, but it's still a trip back down from the server to the display on top of that.