My company is already paying for Teams as part of our O365 Installation. We won't use it, simply because of the network effect the Shared Channels have created.
We have shared channels with Integration Partners, Suppliers, Enterprise Customers... These are extremely valuable ways of communication once setup, especially with simple file-transfer thrown in, etc.
Leaving Slack would mean slamming the door in the face of these entities, something we're simply not ready to do for the cost-savings that ditching Slack would mean.
I don’t know a single enterprise client that enables external Slack users. People are far too careless with what they share in IM (like private SSH keys and IP addresses), and Slack history is a juicy target for hackers diving for secrets.
Enterprise users usually just use it for internal messaging.
If that's what's best for your company, great. For others, competing against MS Teams means that they will face an uphill battle on the sales side - to put it mildly. In terms of the cost savings aspect once MS reaches feature parity-ish, there will be significant pressure on the CIO to consider a migration away from Slack. Both of these pressures raise valid questions about the valuation and future of Slack.
We have shared channels with Integration Partners, Suppliers, Enterprise Customers... These are extremely valuable ways of communication once setup, especially with simple file-transfer thrown in, etc. Leaving Slack would mean slamming the door in the face of these entities, something we're simply not ready to do for the cost-savings that ditching Slack would mean.