[nfd]

Slack and IRC have two different (but interconnected) use cases. I love IRC, and I haunt a couple servers to chill or to ask an occasional newbie question. I'm pretty comfortable with IRC; it's a part of my culture.

I often find myself needing to establish a line of communication between people who aren't particularly tech-savvy. Slack works excellently for this: I make a new team, fire off some invites, and everyone just understands how it works. I can only imagine that, say, coordinating dev, corporate, and sales over IRC would be like living in the same circle of hell cardinally occupied by people who talk at the theater. If IRC works well for your team (whatever it is), excellent! Don't try to fix something that isn't broken. Slack isn't flawless, but it does have its usecases, and it fills them very nicely.