“Last year we began testing a quality filter setting and we’re now rolling out a feature for everyone. When turned on, the filter can improve the quality of Tweets you see by using a variety of signals, such as account origin and behavior. Turning it on filters lower-quality content, like duplicate Tweets or content that appears to be automated, from your notifications and other parts of your Twitter experience.”

New Ways to Control Your Experience on Twitter | Twitter Blogs

This is a bit like the proverbial tree falling in a forest. Does this mean that Twitter now gets let off from policing the trolls?

The troll has still behaved badly, it’s just that the target doesn’t see it. Importantly, the friends of the troll see the comment.

Will Twitter allow someone to study the change? This is very important.