> because Facebook chat is really the only widely used chat service at this point
This is... well, if you consider WhatsApp and FB to be the same then not wrong, but as it stands they're still separated ecosystems and let me tell you, WhatsApp is huge. There's a number of competitors in China and other parts of west Asia that are probably even bigger. Anyway, WhatsApp is used for family, friends and non-work related / event based colleagues.
Then there's Slack, mostly for closed communities (due to their pricing models), which in my experience has improved communication and knowledge sharing within my company by a lot (consultancy company).
Third major chat pillar in my life at the moment is Discord, probably the leading chat platform for open communities and individuals. It's replaced IRC or Skype for a lot of people, especially the gaming community. Because they aim at open communities, I think they have the potential to outrun Slack in short order. If they want to compete they'll have to build a "professional" version that replaces the gaming landing page with something a bit more corporate.
Especially Discord will, in 10-20 years, trigger that nostalgia that people now feel about IRC, AOL, MSN or ICQ.