I don't know, it is quite easy to search a well indexed chat for keywords in order to find important information.
Slack is an attempt at legitimizing and organizing stream-of-consciousness. It has short feedback loops and therefore cannot communicate deep research, novel concepts, nor well-cited evidence.
This is the wrong way to bring the tools of the consumer to the enterprise. Nobody asked for this chat tool - Slack is something sold to somebody who doesn't want to worry about something, not somebody who wants to do something well with low attrition.