Hrm. Mac computers allow this with Slack. The installed version can intercept links to messages in the browser and open them in the app instead of the website. So I don't think it's just phones doing this today.
And I guess Slack is signed on Mac via Gatekeeper, but it's not distributed through an app store.
I don't run Windows and I won't install Slack natively on my Linux boxes, so I can't check the other platforms. But I would be a little surprised if the same doesn't work on them. This is basically how mailto links work today, right?
See https://developer.mozilla.org/en-US/docs/Web/API/Navigator/r...