RC -- read that article and it really burns me up. There are many good reasons to overhaul the current cat system, but creating a cat 6 rating is not one of them!
It is a warning system.
Given the lack of response even to mandatory evacs, and the possible politics involved in issuing one (i.e. NOLA, not issuing one until the last minute, to avoid legal repercussions from not being able to evac those who could not get out on their own, waiting to the point where all they had time left for, was to substitute local shelters instead), the main impetus in revising the cat system should be to create warnings that would motivate people to leave, without being so complex it would confuse them. If the reason would be to provide categorization for mets, that should be separate from trying to devise a good warning system.
Right now I think the next big step that everybody is ready for is to separate wind and surge warnings, and it may also help to focus more on the damage descriptions of each cat level rather than just talk about a number.
Look at Key West. If they'd gotten five more feet of surge, a lot of people would have drowned right in the middle of their party. It might help a lot next time if the mayor stands on Duvall St. and holds up his arm and says, "At 10pm water will be up to here, and by the way the wind will be over 100mph at that time." There must be something that would motivate people. Someone ought to go out and talk to the survivors and ask them what that would be. I think they would get a lot of responses like, "Well I didn't know it was going to be this bad." Then if you sat down with every one of those people and backtracked over the warnings that had been put out, they would find out that the warnings did in fact say that it could be that bad. So what is the language that you use to get across to everyone?
Of course language probably isn't the problem most of the time; there are a lot of people who would have many rationalizations which all add up to not wanting to deal with evacuating (assuming they have the money to evacuate). But I think language might help a lot, in certain cases, because many of the people who died on the MS Gulf Coast in their own homes were older people, who simply may not have understood (you can count my own mother in this category).
Katrina's Surge: http://www.wunderground.com/hurricane/Katrinas_surge_contents.asp