I don't understand how this would make anything better.
I post to "friends of friends". The people who follow my followers see it, but not the people who follow them:
me -> sep1 -> sep2 X sep3
Someone in sep2 replies to my post as "friends of friends".
me: can see my post and the reply
sep1: can see my post and the reply
sep2: can see my post and the reply
sep3 (follows sep2): can see the reply
sep4 (follows sep3): can see the reply
Now say sep3 replies to sep2's post as "friends of friends".
me: can see my post, sep2's reply, but not sep3's reply.
sep1: can see all three posts
sep2: can see all three posts
sep3: can see all three posts
sep4: can see all three posts
sep5 (follower of sep4): can see only sep3's reply
All this does is further fragment the visibility of content in discussion threads that eventually end up public.
Before we start getting into questions like this, how about we establish whether you're assuming reply control is a thing - whether visibility of replies can be limited to visibility of initial post by the OP.
If the answer is no, then all this does is further fragment already confusing public threads.
If the answer is yes, then this is effectively establishing group private message threads where by definition some members either don't know or don't like each other.
I don't like either option.