Amusingly, the OP is the least productive person when it comes to contributing to the actual Acheron discussion, and yet still feels the need to throw needless jabs around. Oh no I'm a hypocrite! =p Some of these other ideas have been pretty nifty, but they still fall prey to being potentially game-breaking.
If he rages all over a 5x5 around his city, that could potentially include the only way out of your civilization, whereas now you can kind of quietly pray to Esus and try to sneak past him.
If he rages late game, and you're the goose, then you're pretty much cooked, even then, and then your epic struggle games get all sadface =(
The other issue is that if he rages after the first person to get Mithril-Working, or the first person to get X amount of gold surplus, people are going to start getting Mithril-Working up to 1 turn left, and researching other stuff until some other poor sap researches it first. Same deal with the gold surplus, except spending it all like a crazy person instead. Like someone else said, this also is a direct hindrance to the Khazad, who benefit from attempting to raise their gold at the early expense of research.
Too many of the ways to make Acheron 'interesting' aren't independent variables, unfortunately, and affect many other aspects of gameplay that would make a game unplayable. And that's usually fine because it happens early, but this would happen 40-80% through a game, and it's at that point that frustration starts to happen.
I think the simplest solution to this would just be to include something next to 'Raging Barbarians' that is a 'Raging Acheron' option. Check or uncheck. Checked removes his held promotion. Problem solved.
