I'm going to go on record saying I think it almost has to have been intentional.
This be a HUGE mistake if it was a mistake and could destroy whatever roll-out they had planned.
Besides, I look at four things that point strongly towards intentional.
1) very little new info in this video otherwise. Basically this was a complete throw-away for the folks that are watching closely if not for the the leader leak.
2) placement of the leak. It's b-roll, having nothing to do with the video or what is being talked about. The camera wouldn't have been in that hallway where it might have caught something taboo if Firaxis didn't want them there.
3) the quality of the leak. It is just good enough that (with it being in alphabetical order) we have mostly worked who's who. Much better, and there would have been no game to it. Much worse and it would have been pointless. And even the fact that they were in alphabetical order is reasonable circumstantial evidence that this was deliberate.
4) the value of the leak. Not only did the leak generate a TON of furious comments and other engagement from the community, has two other benefits. It gives Firaxis insight into the thought processes of its core die-hard fans, and it does so with very little cost. They haven't (and I presume won't) confirm that we worked it all out. They don't have to confirm anything any sooner than they would have otherwise, and if they *REALLY* wanted to, they could tweak things based on reactions here. I don't expect they will, but if they were say on the fence about a particular leader, a negative eruption might nudge them to their next choice.
Which doesn't mean it wasn't a gaffe, but boy howdy is it a big one if it was....