Eichel, Dahlin - actually untouchable.
Reinhart, Jokiharju - practically untouchable. You want to trade Nathan MacKinnon? Okay, sure, Reino can be in that package deal. But that's just never happening, so let's not argue semantics over what "untouchable" means. As for Jokiharju, it's wild that he's only 20. But, generally, when you find players as good as these guys, do not trade them.
Cozens. I don't think its fair to put Cozens on this list, but I did it anyway because I really like his style of play plus his production in junior (production being the key there). Both of those things together give me hope that he can be a valuable NHL player. It was either him or Larsson.
I'll be kicked out of the union for this, but no goalie should ever be considered untouchable unless/until they start putting up consistent Hasek numbers in the NHL. If anyone wants your best goalie prospect in a trade, make that trade. Even the best goalies, with the exception of Lundqvist, generally have wild fluctuations in performance and struggle to maintain success from year to year. Then Matt Murray walks in and wins two Cups, and goes back to being bad again. It's a very hard position to play well, let alone play well consistently.