The Nash comparison is very appropriate, for several reasons. Both Hall and Nash are strong, powerful skaters whose greatest weakness is their playmaking. There is no subtlety to either guy's game ... they are at their best when the situation requires them to fly around the opponent to create a scoring chance off the rush, and at their worst in tight corners when they have to do something effective with the puck. Just watch either of them try to make a backhand pass. Not happening.
After several seasons struggling to become an elite scorer, Nash learned to become a dominant two-way player, in large part due to his involvement with the Canadian Olympic team. He was an absolute beast on the checking line in both Vancouver and Sochi.
Taylor Hall is coming to a similar point in his career that Nash was when he figured out the 200-foot game. Hall is never going to put up much more than 70-80 points (although having McDavid might help with that) and the major concern with him is his lack of defensive acumen. If he is going to take his game to the next level, he'd be well-advised to follow in Nash's footsteps and become a relentless two-way player. He certainly has the speed and size to do it.
Could you imagine Hall and Nash flying around the ice killing penalties for Canada in the 2018 Olympics? Scary.