The opaque string part of the URN is interpreted by these secondary resolvers. The name of the naming authority is essentialy a sub-scheme name for the opaque string, since the naming authority maps to a set of resolution services, each of which resolves the remainder of the URN in whatever way is appropriate. It's false only if everyone runs a proxy. I agree with Roy. Remember, the client can do whatever it wants, and this is true for URLs or URNs.
Caching proxies are essential for the scalability of the web.
Hmm, we're talking about different things. The second stage is directed by the info found from the first stage. On the other hand, one scheme using DNS is not a bad idea, especially one that is very extensible, but it should not be assumed that all schemes need to fit into the same mold, no matter how general. You can't avoid the existence of a scheme. But, again, that depends on what you mean by scheme.