The organizations owning some portion of the name space would maintain that portion and possibly even provide the computers on which it was stored. In fact, the X.509 data record was originally designed to hold a password instead of a public key as the record-access authentication mechanism. The original X.500 plan is unlikely ever to come to fruition. For an extreme example, imagine the CIA adding its directory of agents to a world-wide X.500 pool. That idea requires a single, global naming discipline and there are too many entities already in the business of defining names not under a single discipline.
Legacy therefore militates against such an idea.
What had been an access control instrument was now an identity instrument, along the lines envisioned by Diffie, Hellman and Kohnfelder. The insistence on X.509 certificates with a single global root delayed PEM's adoption past its window of viability. It was distributed and used by a small community, but fell into disuse. At about the same time, in 1991, Phil Zimmermann's PGP was introduced with a different certificate model. The theory was that with enough such signatures, that association could be trusted because not all of these signer would be corrupt.