What about uploading files, video and voice chat, scrollable and searchable chat history, code snippet support? These are the reasons people use slack. To say IRC is a substitute means your company doesn't need to solve these problems (which is fine, they may not have them) or it means you're using a bunch of products together to solve them.

I don't get the stance that this is "hype" or a "bandwagon" at all.

What's a good way to get mobile notifications about an IRC message?