Personally don't see any downsides to this, if the industry can really get around it then it would make 8-pin connectors and any combination of multiple 8 and 6-pin connectors redundant, essentially standardising the input for any GPU that uses over 150W with a single smaller connector. Not like we should ever see cards that *need* two of these, because that much power/heat(500W+) would be impossible to dissipate in a gaming GPU form factor.
Would there be gains to cards using two of these even if they didn't need them? Yes, definitely. Would it be worth the costs