I'm not commenting on whether OStatus will ever have these features. I'd like to just point out that what you're describing is absolutely disturbing. I'm talking about the part where you said that these people cannot be reached the other way and conduct all of their conversations on Twitter.
Well, let me clarify just in case: the “impossible” is an exaggeration, since they will eventually respond to things like email, but it's not enough to keep up. Many of the socially-important multicast messages only occur on Twitter. I've been meaning to subscribe to them with a local aggregator, since for those whose tweets are publicly visible that should be sufficient, but while my existing RSS links still work, I can't find any way to acquire new ones, so right now I'm reduced to manual polling.