(Not directly applicable to Twitter, but to online communities in general)
It'd be interesting if you could have two votes: whether you liked what the person posted (which would only be visible to them) and whether you'd personally share it with your friends (which would affect it's ranking only among your friends)
Or put differently, I wonder if it's not possible to create a system that dynamically sorts content, instead of having static groups. Seems like static groups with a label on them inevitably end up arguing about exactly what the label means (grin).
I don't want an echo chamber, and I want to be challenged -- but I don't want a daily rage fest against whomever the internet currently hates either.