This is actually quite a smart idea, implemented too little and too late to make any real improvement. The reason One of the reasons I think Twitter became such a toxic place is because the public-by-default model made it so easy to share your private thoughts with complete strangers with very little filter, intruding into their private thoughts, utimately causing them to voice their opposition with very little filter of their own.
But then again, if you took that model away (or de-emphasised it to the point where it was no longer the main point of using Twitter), then it wouldn't really be Twitter anymore. I kinda feel like people only go on Twitter to enjoy that toxic soup of unfiltered opinions, stir the pot and occasionally add their own.