It seems Donald gave up on this thread, but I'm still struggling to make sense of this new rule. I'm trying to figure out how it can be expressed in my rules document. I was hoping for a clear answer to my question about mandatory and optional abilities.
Part of it is that I'm struggling to fit Donald's explanation of how this makes sense into the existing rules. To me it just seems like a completely new rule that needs to be added and explained. It follows from the printed rules to a much less extent than the old rule did. (I'm going by the 2nd edition rulebooks.)
It makes turn order for reactions very different from turn order for other things. There is never any reason to go in turn order except for the risk that everybody passes. If player D happens to react first, and this makes both B and C want to react, C can perfectly well react next, and then B.
Let's say we all have Diplomat and want to react, and some players think the order matters. The printed rule just says, go in turn order. The natural interpretation is that if the first player wants to do it, they have to do it first. But with the new rule, they can wait and see, risking possibly that everybody else passes too (assuming that they players know that this is how it works). As far as I can understand, there is never any "if we both want to do something, we go in turn order." There is only, "I want to wait and see what you do, but since I'm before you in turn order, that could mean that I don't get to react." The turn-order rule has been reduced to this very specific wait-and-see rule when it comes to reactions. (If you're not doing wait-and-see, the turn-order rule has no relevance: You can react several times whenever you want before or after the other players react, just as if there were no turn-order rule.)
Here's a related problem: Under the old rule, usually everybody just reacts whenever - out of turn - and it's usually fine. This is the same under the new rule. But under the old rule, it's technically incorrect. When the players realize that the order matters in a real-world scenario, someone - maybe several players - would often have reacted already. Under the old rule, we backtrack and everybody has to do all their reactions in turn. Simple. Under the new rule, the reactions that already happened were technically not incorrect. It's perfectly legal to react out of turn. So following the rules strictly we shouldn't backtrack. (And when players are in this situation it's because they realize that they have to follow the rules strictly.) I guess a player could make the argument that they actually didn't want to pass but wanted to react first, etc, and we could then agree that it's fair that we do backtrack and go in turn order. Kind of like when someone forgets to topdeck a Treasury. But to even realize why or how it's like that, seems very difficult and complicated.
But let's say that the players do agree to go in turn order. Well, then we have the following weirdness.
Let's say we have 4 players reacting, and we decide to go in turn order. First it's A, who passes. Then B reacts, which means everybody else gets a chance to react now, before we move on to C. First A, who passes again. Then C, who passes. Then D. Since we haven't reached C in the outer loop yet, C will get another chance, but D could react now, if they want to do it before C. Let's say D reacts. Now we start a third-level loop, A + B + C, let's say everybody passes, and we're done with the third-level and second-level loop. We continue in the outer loop with C, who reacts. Now we start a second-level loop with A, who also reacts. Now we start a third-level loop with B + C + D. Let's say all pass. Now we continue the second-level loop with B + C + D. D is left in the outer loop, but we can ignore that, because D was the last to pass. If this is how it's supposed to work, it's crazy. But maybe I'm not understanding it.