Yeah, something's kerflooey here. I don't see how a TDP of 500W is feasible with only air-cooling. That's about 4x too high a number, unless the air is chilled first. But there are multiple sites that report NVIDIA as having stated those specs.
You state "Nvidia is now promoting its latest Pegasus SoC, scheduled for delivery in 2018, designed to perform 320 TOPS — more than 10x the performance of its predecessor — at 500 watts of power." AFAIK, the Pegasus is a board with multipe SoC's. I am not aware of any single SoC that can dissipate 500W.