I know this sounds crazy, but hear me out.
There was a significant level of exterminationist sentiment among Americans towards the Japanese (10-20% of Americans thought that all Japanese should be killed). Many US military leaders used genocidal language ("Kill all Japs", etc.). But people say a lot of things and the war in the Pacific was particularly brutal, so this was probably just tempers running high. But the US military also plans for lots of contingencies that never occur. For example, I've heard we had plans in case we get invaded by Canada (this may be apocryphal but you get the point).
So, my question is: Did the US military ever plan for the contingency that the Japanese would never surrender and would "need" to be exterminated?
The short answer is no, at least not in the industrialized sense of the Holocaust. While the US did perpetrate plenty of crimes against both the American civilans of Japanese descent interred on the continental US and against Japanese soldiers in the course of the war, there is basically no comparison to the many steps and processes which led Germany to rationalize the need to exterminate world Jewry.
While there was indeed plenty of racism against the Japanese, this was built more on nationalistic stereotyping than actually defining them as a pest. Remember that the Final Solution was just the end result of over a decade of dehumanization and marginalization, built on an already existing bedrock of antisemitic thought from the middle ages and onwards.
As far as I know, there was never any doubt in the minds of US command that the Japanese center of gravity could be broken, and an unconditional surrender gotten, even without the atomic bomb