No matter how good the netcode is, you're still going to be subject to the non-avoidable issue of the data being routed through the freaking Earth. Even at the speed of light, which is what they travel through in the underwater fiber optic cables, they still take time to get from point A to B. Even with Killer Instinct netcode, USA to Japan is gonna be unplayable.
That is unless we invent some faster way of carrying data, or invent Faster Than Light travel.