Everyone who uses VOIPs (vent, mumble, teamspeak, etc) are already doing this. The only difference is the person calling out the abilities is doing the fighting as well. If anything what they can do is allow spectating with a delay of 30 seconds. That way it's not live to the second, but they can still see the fight unfold.
It's not different than watching a video on YouTube with a commentary which would make any in-game recordings or spectating almost pointless. Spectating could serve as a way of having someone watch you and help make suggestions for the next attempt, but at most that would be it.
