Re: Japanese Giant Robot
I seriously doubt that humanoid combat vehicles will ever replace tanks, because at ANY given level of technology, even future levels, tanks have a lower profile, and more importantly, have a better volume-to-surface-area ratio and a MUCH simpler drivetrain.
Yes, it's possible and even likely that advances in armor, power generation, and actuator/motor technology will make a "giant robot" possible, but those advances will ALSO be available to tank designers.
This doesn't mean that mecha will never exist or that they will never have any role on the battlefield, though. The anime series "Gasaraki" depicts an interesting and relatively realistic version of mecha which can't stand up to a tank in direct combat, but can take advantage of their superior mobility in urban environments.