non maliciously this is occasionally a problem. different registrars have different rules, some will delete a name after so long the destination is dead, others wont. so registrars will let you register an abandoned name with a new destination, but some wont. But local address books will default to the older destination over the newer one.
i think it was done this way so there could be no one thing declaring google.i2p goes to a destination, locally you decide. wouldn't be a bad idea to incorporate some sort of cert though, a lot of that work would fall to the registrars to agree i'd think, like on expiring names.
i think the idea of using dht for this so it's more like a network consensus thing has come up, but there's reasons not to do this.
definitely opens up another surface for attack, could see flooding namespace, sibyl, hijacking consensus mechanism somehow, lots of very bad content would surface too which some of the current "curators" try to dampen. Consensus mechanism would be tricky to get right