What I think is a better idea was proposed here last year, and I think someone was doing it for a while. It is for someone to volunteer to be the keeper of the remailer aliveness information. He runs scripts every day to ping the remailers, keeps lists of which remailers are currently active, and so on.
This does seem like a better idea, except for one thing: Everybody has got to trust the Keeper of the Aliveness Info. I'm not sure how much of a problem this is, nor am I sure that the newsgroup method neccesitates any less trust. But I do think that a system where all trust doesn't lie in any one entity is desirable, and I think that such a system is going to have to be decentralized like netnews, rather then centralized . The other problem that a centralized system imposes is that if the Keeper Of Aliveness Info goes down, everyone is scrambling to find a new one. This doesn't seem like a major problem, but again, an ideal system wouldn't have this flaw.