The thing I think with #3 is not that it is a hot button issue, but that it could be quickly. Baseball has blessedly been very liberal in letting the Pitch/FX data be disseminated to the public - both via the gameday stuff as well as just for analytics. The league knows how important that stuff is to a lot of people (baseball is uniquely built for that - big part of its tradition). But you disseminate that and you are also sharing just how dreadfully, blatantly wrong the umpires are, every single night. I am not sure how long they can pretend the state of calling balls and strikes is okay when there is so much damning visual evidence.
Now the task is impossible. Between issues of tracking the ball flight of an 80 mph pitch (to say nothing of a 95 mph one), watching the swing of the bat, and general depth perception ... the best umps in the world can only get to (collectively) about a 6/7 level. When one sees how important the count is to the success of an at-bat, mistakes change things, all the time. Now - I understand this sort of large error margin is there in other sports - offensive line infractions in football, off-ball fouls in basketball, almost every minute of a hockey game - but there is existing, mature technology that would bring the error rate down a lot, and it could be implemented within a week.