This may be the dumbest thing ever, but I would love a version of Twitter that only let me post and retweet after a sufficient delay. For example, if I go to retweet something that's breaking news, start a 24 hour countdown and then make me confirm the retweet the next day. Similarly, when I make a new tweet of my own, make me wait at least 30 minutes to post it. Again, only tweet it if I still want to send it 30 minutes later.
Obviously this won't appeal to everyone, and sometimes there are situations where the quick communication of Twitter is essential, even a matter of life or death in some cases, but I personally would love this feature.
Sometimes I'll think of somethng witty to tweet out, I'll type it out on my phone and get distracted by something before sending it. Then I open Twitter again, see the draft I was going to post, and think, "what was the point of sending that?" I almost always delete the tweet. This idea is really an automated way of doing just this, and I suspect most of our tweet volume would go down by half if we let things settle for a bit before posting things.
People sometimes act like outrage and fake news is only a problem for Twitter and Facebook, but it's a problem for any form of social media, as these services live and breath on those quick dopamine hits you get from posting some witty rejoinder or boosting something that supports your worldview. After all, on social media we can all be experts in whatever we want. This feature would not fix that entirely, and most people would never use it, but I would.