Did you consider making the name cache even more central like kded or
kdeinit? That should give us more cache hits in some cases.
My first try to integrate the resolver into KIO was via a standalone DBus service, i.e. I wrote a DBus adapter with "delayed reply". The result was completely disappointing because of high latency. Besides, I doubt the session bus is apt to handle the slave storm usually triggered by Konqueror. So I think a kded module is out of the question. The location in the application's address space is of course not forced, but allows fast name resolution without much additional complexity.