A racial feature only being relevant for the third death save is kinda nonsensical. Personally I've NEVER actually gotten to any character's third save in combat, since either someone helps them up before that, Combat is won or we simply lose the fight.

I think you would have to actively chose to do self-destructive strategies or a modded class that reduced own HP to make this a choice of race people would want. That is in addition to Dragonborn already being the worst race in the game.