The hard part's not creating some kind of certification, it's getting desirable employers to accept it as a replacement for the most-painful parts of their interview processes. I suspect a lot of top companies don't want to make it easier to jump between them.
The "most painful" part of any interview process is just the part that you happen to be the worst at. Personally, I don't find leetcode to be painful at all and would be much more enthusiastic about something that eliminates any part of the interview where you have to talk about yourself.
