First, let me compliment the erudite entries which I've read with interest (and the occasional twinge of envy), my own contribution I fear is much more minimal.
The real problem as I see it, which has been touched on many times, is not so much the attack, type of attack or even the type or number of attackers, but rather endgendering the correct feelings in the person attacked. That wonderful, mind-numbing "oh s**t I'm going to die" trip which can make a stunned bunny look positively proactive.
With relative beginners, it's reasonably easy to get the andrenalin response - real weapons practice an obvious answer. However, how do you maintain that edge of fear and "authenticity" (nice word, I'm borrowing it) with people who've practiced together for years, even assuming the attacks are committed?
Without adding a "death by misadventure clause" to the dojo rules, I don't think it's possible and the only thing I've found helps in a "real" situation is practice until the brain isn't involved. The attack shouldn't matter, the weapon used shouldn't matter, you should have moved before you've had a chance of thinking, which of course means practice until you're too tired to think then try the "hard" stuff and practice some more.
(One of these days I must take my own advice on this)