RoBirk29384 has a good point. :yes: We've always had difficulty levels in Zelda, and they are both completely optional AND customizable all in one, as such, we are not forced to choose from a list! (e.g. Easy, Medium, Hard)
This is my point. Zelda is the phenom of its genre due largely to its accessibility and options. The game can be played in any fashion the player wishes. The 3-heart challenge surfaced due to these options. One is not forced to increase their health, but may choose to do so. In forcing ones hand, as most games today do, you remove something from the gameplay that has made the series as fantastic as it is. A 3-heart challenge mode would remove much of what makes Zelda the franchise it is. As said before, this involves the removal of exploration elements, shifting the genre of the game from Action-Adventure to Action.
Again, I use Metroid: Other M as my example:
Aside from the redundantly bland story telling, it was a solid Metroid game, packed to the gills with everything we love about that classic side scrolling shooter, and the massive amount of exploration involved to experience the game to its fullest. Then there came the Hard Mode, which decided to take everything that made the game a Metroid experience, and tossed it out the window for 5 hours of repetitive "point A to point B" action. Every pick-up had been removed, hightening the difficulty, yes, but taking away the gameplay that, until that point, was essential to the franchise.
Metroid is similar to Zelda, particularly in the fashion of the Prime games, where pick-ups and upgrades are largely optional. A hard mode doesn't need to remove incentive to go off the beaten path, particularly when the option to avoid such power-ups is certainly available to the player for a hightened difficulty, customized by each individual. Much like Other M's hard mode turned the game into Metroid meets Ninja Gaiden, the inclusion of a forced 3-heart challenge hard mode to Zelda would create a similar tension, pulling Zelda away from the genre it has defined.
Off topic: To whoever gave me bad rep for my thought out opinion, please understand that it is mere opinion, not unlike Axel's post involving his distaste for Operation Moonfall. To disagree is sporting, but to attack one's opinion is just immature.