I think the idea of an enhanced rating system sounds great in theory, the problem is implementing it. There are countless variables involved.
Take, for instance, Stowe's Nosedive. It starts out narrow-ish, curves through three turns and then widens out. There's no getting off -- i.e., once you're on it, you're on it to the bottom (2 miles, 2100 vertical feet, more or less). Top is steep-ish, bottom flattens out considerably.
On a bright sunny day any strong intermediate could ski it without a problem. When the clouds have rolled in and you can't see five feet -- the steep turns at the top get a lot more challenging. In the afternoon and the hordes have skied it and the trail is in the deep shade -- the challenge is upped another notch.
So what would be the rating on this trail? Groomed, single easy black, narrow+steep for a few hundred yards but then you're ok until the afternoon or if it's foggy? Did I mention that there's sometimes a bump line on the side through the upper turns?
People keep saying there are countless variables to include, but the vast majority of them are irrelevant. Yes conditions will vary, and the angle of the sun will change, and maybe you didn't eat your Wheaties for breakfast, but there are several significant factors that aren't changing that could greatly effect a skiers decision regarding what trail to ski. Rate the trail based on the most difficult section of that trail. We already see trails rated as blacks that after the headwall, will level out and ski like a green, but because there is no other way to access that part of the trail, the whole trail is considered black. If the trail is rated based on the worst case scenario for that trail, it would prevent skiers from getting into trouble on that trail.
You can't really deny the fact that if given a sense for the pitch and how wide the trail is, a skier would be better equipped to make the decision as to whether or not they are comfortable with attempting that trail. Sure you can worry about how long the pitched section is, and there are quite a few other variables that could be considered, but how would more information be a bad thing? On a bright sunny day with ideal conditions, an intermediate skier could probably handle most blacks, but on a low light, icy and windy day they might struggle on most blues. But if they know that a trail is steep and narrow, it will let them decide if the conditions on that given day will allow them to step up to the blacks, or step down to the greens. As it is now, they still face variable conditions, but they have no idea what difficulties are ahead of them on a given trail.
As for the trail you describe, I don't know what the rating would be. There isn't a uniform system for designating a trails difficulty. At one mountain, it could be a blue, at another it could be a black, and at another it could be a DD. That's why we are having this discussion. But since you tell me its narrow and steep for a few hundred yards, I can evaluate my comfort level on narrow and steep terrain and make an informed decision. If it gets foggy, I can make a decision as to how comfortable I am with a steep and narrow trail in foggy conditions. Under the current system, at the mountain that might call it a blue, an intermediate skier would attempt this trail, and struggle with it, possibly get hurt, and have a miserable time. Where its rated black, that same intermediate skier might steer clear of it all together, but if hes feeling good and conditions are good, he might try it. Where it is posted as a DD, that same intermediate skier will probably stay away.
The way it works now leads you to assume that a blue is less difficult than a black, but based on what people are saying in this discussion, that's not even true. So why wouldn't adding a little bit more detail to a trail rating be helpful? It would have to be better than relying on a system that is at the least misleading.