The reason I think it's really dangerous to allow such a maneuver is that if I'm driving in the right lane on the 2-lane half and I'm behind a slow car, if I have a dashed white line on my left, I should not have to look for conflicting oncoming traffic ahead of me. I would think people who might want to cross a dotted white line should have priority over people who might want to cross a dotted yellow, especially because the passing lanes are often coordinated with terrain where there's more likely to be slower traffic.
If you allow that, you might as well stripe it as a true suicide passing lane where neither direction has the right of way, which I can't imagine is allowed in the US anymore...
And I can see this being why it's not universally allowed. On roads like this, at least out here, they're wide open, even going down the mountain passes, you have great sight distance, and not huge amounts of oncoming traffic. We all saw each other, and it was a non-event. I can see this being very different, say out east, or in more populated areas. People who have ridden with me, who aren't from around here have looked at me oddly when I've made this sort of pass.
One thing that almost seems undefined, is which side has priority? My read, is the uphill side (who has a white-dashed line) has priority, meaning it's incumbent on the downhill side to yield.
On the mountain passes, sometimes one gets behind a truck who in many cases has different speed constraints than I do. This specific area isn't the case, but Wolf Creek has a different speed limit for cars and trucks. I have a little more maneuverability etc. in a smaller car, so I can zip around him when safe to do so, and happens all the time without incident. The car coming uphill sees this, is hopefully KREPT-ing (and on the passes, pretty much everyone does), and it's really a non-event. If I look down, and see a pass taking place on the uphill side, then I just wait.
unrelated, but sort of related: To the truck drivers who manage to keep their s--t together on these passes, the utmost in respect.