If they add more than one challenge per game, I will flip out. Not a fan of challenges that you get back on overturns either. I don't even mind the game taking longer; that's not the problem. If the # of challenges exceeds the average number of blown calls that drastically change a game (somewhere between 0 and 2) then managers are just going to challenge every time they can; this will ruin all strategy involved in deciding if you want to use a challenge or not, and make the whole system boring. If you get rid of the drama surrounding blown calls, you have to replace it with something to keep the game as good. That something is the strategy behind using challenges. More than 1 or 2 challenges = no strategy = boring. We don't yet know if replay is going to make the game suck, so even if you want more challenges, just keep it to one per game for the first year.
On the strike zone subject, they should call the high strike again. The whole point of the strike zone is that it's the area where a batter can realistically get a hit. With the umpires' current incorrect strike zone, there's an area above it where you can hit the ball, but it isn't in the zone. This incorrect strike zone takes the drama out of a fastball being painted at the top of the zone, because the batter could have hit it even if it was high. I like how it's hard to decide whether or not to swing at a high fastball with the actual zone. They should go back to the old zone by continuing the thing where umps are rated based on performance, but make calling the high strike part of this. Umps that successfully call the textbook zone will be allowed to ump important games such as the WS and the all star game. Also, going by the textbook definition will create much more consistency than "the top of the strike zone is roughly a baseball's length lower than the letters. It's kind of right here. You just have to kind of learn where it is."
I'm also not in favor of the electronic strike zones mainly because they are quite inaccurate and don't take the batter's height into account. Even if you programmed the strike zone readers to take the height into account, you could never tell where the zone is because everyone has a different posture. According to the textbook, the posture used to figure out a batter's strike zone is the one they have as they prepare for the pitch, right before it is thrown (I think). To make electronic zones law, you would have to actually change the definition of the zone to make the top and bottom a certain percentage of a batter's height. Electronic zones would also just suck the life out of the sport; no more ump noises, just the sound of the ball hitting the glove, lame.