Of course, it gets really hairy really quickly. Technically, a perfect runahead/negative latency requires ([all possible input states] to the power of [amount of frames of lookahead]) frames to be rendered.

A single player NES game has 8 binary state controller buttons, so 2 to the power of 8 input states. You need to render 256 frames for each frame of runahead.

Now surely you're thinking you'll just prune the set of possible input states through smart prediction of what the player will probably do next, but it doesn't matter. The number very quickly grows to ludicrous amounts of processing for anything that isn't an antiquated console. Let alone for 3D FPSes that use float values for e.g. mouse state.

Edit: and I should add that if they even try to do this, the amount of CO2 they'll waste is going to be horrifying.