> So they have to close everything off, to make sure that people can't extract their conversations out of the silo.
I totally agree with article itself, but this is rather moot point. Slack still provide full history export for free and it's rather easy to self-host said history. IRC and XMPP didn't made it any easier to extract that data.
I aware that export doesn't include private messages, but it's not what Slack used for mostly anyway.