The only thing Slack provided for the longest time was chat. Essentially it was nothing more than a decent, private IRC implementation. I'm curious what your DevOps team found as a pain point in communication. Were you just using email?

Slack now is a significantly improved tool that we use all the time for everything except large or external video chatting. It's a very nice tool for centralization of alerting, monitoring, etc. We'd find it very hard to move elsewhere as a company.