What If... Slack Showed "Seen" Indicators

Probably a bad idea for work environments, but what if Slack showed a "seen" indicator whenever the person saw the message. This would be hard to measure since the receiver would have to be active within the Slack window for the program to know the user was recently active but some us have Slack in one window and can even read messages without ever "activating" that window. Something to think about but imagine how disastrous things could get.