Do they now have concealed carry in Australia? News to me. If only one of the hostages had a gun and used it on the perp, perhaps the perp would not have used a shotgun to kill two people and wound others. He would have died fast and the cops would not have been involved, except for clean-up.
That's not a concept that really exists here. If you have a handgun licence, you can carry a handgun, concealed or openly. We don't make the distinctions Americans do.
But handgun licences are rare. Partly because they are not easy to get but mostly because very few people bother. I do have one but I don't know many other people who do. Then again, I might now know in a lot of cases. But they are rare. 1 in 100 people would be an overestimate.