It's currently impossible to reconfigure a replica set from a configuration object that specifies all localhost (or loopback IP addresses) to one that specifies no localhost (or loopback addresses), even with force: true. If the point of force:true is that the user is expected to know what he's doing, this might as well be a supported operation. (As improbable as it seems, user got himself into this situation during a training session today, after exhausting disk space, and getting out of it was annoying.)

Alternatively, maybe we should just not let people use localhost/loopbackaddrs for replica sets entirely?