I have been anticipating this, and hoping that we could skip over the "challenge" era and just proceed directly to a fully robotic zone.
With so few challenges, whereas umps typically mess up about a dozen pitches per game, this still leaves a lot of distraction and time for argument. And, virtually any time a player argues, he is instantly thrown out of the game. The umps have all become extremely impatient with this, no matter the tenor of the conversation.
More importantly, the pitches that are the most interesting as a fan are not ones that are compatible with a challenge system. When a pitcher can 'paint' the edge or corner of the zone, so that just a small fraction of the ball is over the plate, it's a great thrill. Likewise, if a batter can work the count by holding back from a close call, it feels way better if they are rewarded for that, than if they are penalized. I think they can turn the strike zone into a really compelling aspect of the game, even more so, and by the way doing this properly would make it 3-dimensional.
The calls from behind the plate actually do determine the winner of a game pretty frequently. It also happens in the playoffs. And once that becomes apparent, you tend to lose a lot of interest in watching. NBA and NFL have suffered mightily from this problem. They're ok financially now, but it's still not necessarily an enjoyable product. I think baseball has done well to lead the way forward - they have lots of new rules that they're loving even when they are not popular. And this idea of this particular tradition being really important to people I think is probably concentrated a lot in the people who actually work for the league. The umps need to be fast but they also need to be subject to good reviews, and I think they appreciate it when they are.
Another thing I nearly forgot. The catchers of the league have made two massive adjustments to their entire approach, just for the purpose of framing pitches better so they can "steal strikes". First, they all set up with one knee on the ground, rather than squatting. This is part of the reason they can no longer throw out runners who are stealing second base. Second, they often creep up closer to the batter so that their catch point is more central to the plate. This doesn't lead to collisions very often, but it's kind of not cool for those guys to be jockeying for that territory, and when they do hit one another, it's obnoxious to untangle the interference calls.
I have always loved the NHL model, where only the team captain can speak to the ref. Trying to watch a basketball or soccer game? Sounds fun .... until I see the guys all start whining, gesticulating and caterwauling. Baseball players aren't quite so pitiful - but I assure you I am not tuning in to watch these men complaining to someone who will then do nothing to help them. Frankly it's much more badass to have a respectful demeanor towards the officials.
As cameras have gotten better, computers, and as clips are being circulated more, this topic has ballooned - and while one umpire (Angel Hernandez) retired, we still have CB Bucknor ruining peoples' days with regularity. The league/union had the chance to try promotion/relegation to get the best umps into the majors, and did nothing. I'm grateful that this system is moving forward. But I fear it may not give me much relief, and I doubt it will motivate my homeys to begin watching baseball.