Simply i think that there should be a Master-quest for each new Zelda game and it should be unlocked after you complete it......
Having difficulty options might confuse players and after you have chose your difficulty you might regret it later on (even if you could change it while your playing this would be abused too make easier situations) I think Zelda has done pretty well without this added option and too make Zelda games harder but still to appeal to a wide audience they need to balance out the game, for example hints and tips from in the game to help beginners and obv the game is much harder if you complete it 100% anyway. So if you need to add more difficulty for veterans just add Master Quest at the end of the game for added repeatability and more challenge.
So? If someone wanted to play the game that way, why shouldn't they? You don't have to do it, but if someone else wants to they can. That's why I think it being adjustable in-game is a great idea, it gives the player more ability to play how they like.