Here's the thing about favoriting tweets – it's kind of a personal thing.
I know 'personal' and 'Twitter' don't really meld, but bear with me. There are many reasons why someone would favorite a tweet. Maybe they like it, maybe it made them laugh. Maybe they want to remember the tweet. Maybe they want to revisit the link mentioned in the tweet – to read a news story or find a recipe. In that latter example, we see favoriting as bookmarking. I'd say this is a very common use of the fav.
But there are exactly zero reasons why I'd want to see tweets that people I follow are favoriting in my main timeline.
That's exactly what's happening for some users, however, as Twitter appears to be running a test.
Putting faves in timeline is not OK, but I am nonetheless amazed that "Tweets users they follow favorite" is a meaningful English sentence.
Twitter is also showing tweets from people that people you follow follow – but that's been going on for a while with a small subset of users. These new tweaks to the Twitter timeline are now being pushed to a larger swath.
It's hard to make generalizations, and they are usually incorrect or at least unresearched. But I feel pretty confident in stating the following: nobody wants this.
Twitter already has an activity feed, which unearths news of tweets people favorite and new users people follow, and most people's main timelines are already crowded enough – with tweets from hundreds and even thousands of people plus the retweets they make.
Also, I don't want my followers inundated with my favorites in their main timelines. In a world where people still don't understand that retweets do not equal endorsements, this favoriting thing is going to lead to a lot of confusion. That's a certainty.
Twitter wants more engagement from the flock. These are clearly methods to show users all the cool content they're missing and to get them to follow and interact with more users. But this is something that nobody asked for and nobody wants. Leave this one in the garage, please.