chainBB has the same capabilities of only allowing posts from chainBB to show.
I'm hoping we see that feature on Steemit at some point in the future. I think twice about writing forum posts right now because it also goes out to all my followers on Steemit (and sometimes I don't want that).
Mm. Same here. It's funny that, currently, Steemit is the main barrier to adoption of other Steem apps, haha.