Well...I actually think people don't filter with RSS is the problem. They follow feeds that dump articles into their reader like a firehose, creating noise, esp when everyone sees those same articles on aggregators, twitter, Facebook etc. I think the value of a feature that lets you follow domains rests in only letting you follow domains that post sporadically, if that makes sense.
Hm. So I think we might be talking about two different things. I was imagining that adding domain-following would be akin to following a tag: if someone posts with that domain, it shows up in your feed. I didn't envision porting RSS into Hubski. I think that would be bad, unless as you said, it was from low-frequency sites.
An I was thinking that you'd have content from followed domains not posted by a human. If its just following a domain that people also post, that seems like it would be decent, although with enough users, it approximates the RSS "problem." A lot of users probably wouldn't even define it as a problem though...