Meeting points:
Lots of discussions here and there, it's best for you to listen to this directly
We are very close, 
Right now we use is_greyed and is_hidden for different causes and let the front end kind of make what they want of it and figure out why the post is in this state is would be nice to have either "muted" bools, or a "is_muted" and a "reason" field
We discussed a few different problems and solutions, I think we'll end up with an extra column in hivemind to indicate the reason why a post is muted or not. And change the api calls to return that information. On top of it we'll probably add a parameter for all posts to return muted posts or not, which would improve performance a decent chunk.
@howo