According to Kristina, the member _id fields in the replica set configuration object aren't used for anything, and they're a nuisance any time somebody needs to deal directly with the configuration object. If they aren't used for anything, it'd be nice if they could be left out of the configuration entirely.

(My specific gripe is that when training replica sets, eventually you have to show people the config object, and people tend to ask why the member _id is there. So unless it is or will be used for something, it might as well go away.)