This is all well and good, however, when you have the level of money running through sports that we do today, the motivation to cheat is simply too high to expect all athletes to be clean. This doesn't just apply to running, the problem is way worse in other sports. This isn't just a hobby for these guys, its their occupation, its how they feed their family. Its not just the guys at the top, think of all the runners who race the lower tier races just for the prize money, think of all the domestiques in the tour de france who need EPO solely to complete the tour. They're probably more likely to cheat, their career depends on it. Its pretty dismal, but its naive to think that we will ever get to a 100% clean sport.
What they could do is to make a clear set of substances that make someone dirty and the test used to find them. If the drug isn't on the list, its legal, if its a gray area, its legal. No TUEs of any kind. If you have asthma, too bad. There's no difference between that and being born with more fast twitch muscle fiber. If you are caught with any of these substances in your system, you're dirty. It has to be black and white, and the penalties need to be harsh (lifetime ban), otherwise the policy is impotent. I realize it doesn't really work like this, but if you want a clean sport, this is the only way. The acceptable ranges are what making the waters murky.
I my opinion, this will never happen. I've come to terms that there are athletes that will do what it takes to win. It'll eventually get to the point where its a joke, like how the NFL is today. There's nothing normal about any of them anymore. Doped to the gills and I'm not sure I care.