I re-read the original post and I think he is refering to the archives of the old phpbb forum.
The original phpbb searchengine is not real good and puts a real strain on the server, that is why it is disabled in the phpbb archives. So I think you will never see a real good searchengine for the SubSim phpbb archives. Unless some one will be paying Neal for all the additional costs.
Ah, yes, forgot about that. But do they really contain threads that are not listed in the active forums ?