Predictably, everyone started talking in Slack like their jobs depended on it. Everyone was responding to everything. Instead of writing out a complete message and pressing enter, they'd send each fragment of the sentence as a new line.
The Slack leaderboard was never shown again. Unfortunately the habit remained because people were afraid they were going to be secretly judged by how much Slack activity they generated.
I expect the same thing is going to happen at companies who had token leaderboards. Once you've instilled that fear in people, they internalize the expectation.