I don't think that plausibility is THE priority in alternate history stories. There are plenty of alternate histories that would be very plausible that would be boring as hell to read/watch. They still need to be entertaining, and typically have dramatic concerns like any other form of fiction.
I think this is why
@Campbell said that plausibility doesn't really tell us much on its own. I mean... if there's one thing in this thread that it seems that we'd all agree on is that we want some amount of plausibility or logic to be considered when a GM determines outcomes or other elements of play.
Then why not just let the dice fall where they may?
When can something implausible happen? Or less plausible than many other possibilities? When does/can/may the GM decide that's what happens?
I mean... really bonkers stuff happens in real life all the time. How can that happen when plausibility is THE priority?
Sure, I get that. I was offering an answer to the question, not necessarily the answer or even my answer.
Although this touches on something I mentioned earlier in the thread... dozens if not hundreds of pages ago... that I think the idea of a neutral GM is potentially outdated for a lot of modern play. It certainly has its place in certain games, but I also think it is applied a lot more broadly than is actually suitable to the hobby at large. This is of course dependent on the game and the group, but it's something I've noticed conflicts with a lot of modern game design.