This feature request is still being reviewed by the feature team.
-WarrenPatrick Brooks commented
@Warren : Imagine you have a particular channel visible almost all the time, but it doesn't get many messages. Now imagine that someone sends a funny, animated gif to the channel. You see it and laugh, and then go back to what you are doing. Two hours later, the gif is still animating ... and you can't stop it. What once was funny is now tired and annoying.
Slack provides a command called /collapse, which hides the animation under a tree gui widget ... click a triangle, and see the funny animation again ... click the triangle again and the animation is hidden.
This feature is all about allowing fun things to be sent to a channel, but then allowing users to hide them after they become annoying.