Why gorilla arm? This doesn't necessarily require lifting it. There's an old video around with Zuck doing gestures while walking and he starts with his arm mostly at rest. Even in the worst case, how is it more tiring than a phone?
Gorilla arm is caused by briefly pointing at things in front of you in a repetitive manner. The problem is that this is such an easy to code, universal gesture that it creeps into every interface.
