Nice article on the extensibility of emacs.

On the particular case of slack, using their irc gateway one can use any irc client, which probably has already some kind of distraction-silencing method. Also, IRC bots are now slack bots. As another emacs' extensibility showoff here's an example for temporarily ignoring users[1].

Unfortunately, slack is adding more and more features every day that do not map easily to IRC.

1. http://puntoblogspot.blogspot.com.es/2014/11/temporarily-ign...