This certainly a poor design for a “universal messaging” app. Users are individuals and do interact within several different social circles or teams, and we shouldn’t put the burden of multiple accounts on them as a penalty. The argument that different teams (or organizations) have different constraints on usernames can be resolved with multiple aliases per account. We’re really talking about how “account” is defined. I think the bigger question needing asked is “does Slack’s team construct work generically for individuals as well as specifically for organizational teams?” It feels like it is a stretch to try and fit all my team, family, user group, topic interest into Slack teams. I get request for teams on learning Swift, on Scala, on DevOps, etc in addition to the actual “teams” that Slack was designed for.
Why is it that we as users or consumers try to shoehorn much of our online interaction into the latest fad service? Maybe we are really ready for an online service that is designed for “universal messaging” rather than reeled us in on a specific hook, like teams.