I wonder how hard it would be for a human brain to adapt to controlling 2 extra limbs? This kind of tech coupled with something like Neuralink seems like an excellent field of study.
Of course, it depends on the level of proficiency you want to reach. But it's already hard enough for people to eg learn to play Tennis, or learn to play Tennis with their left hand, when they normally use they right hand.
Driving, cars, flying airplanes (including sitting 10m+ off the ground in cockpit in a 747). Things like playing ice hockey, kite surfing etc. Highly complex activities (including interacting with several others and even plan ahead), often performed at speeds way beyond what a human can move about.