What’s New in Microsoft Teams | Microsoft Ignite 2019

I'm going to be a little picky/rude here, but to restate the title of the request:

"I want to use multiple Teams accounts at the same time"

(emphasis mine)

Adding multiple accounts to android and iPhone then "switching" may have gotten faster, but it's not the ask.  It never was (you can read comments where people expressed this concern when we were told it was the first goal). The ask is that users don't want to switch at all but rather have simultaneous access as needed.  Best example I can give would be a messaging classic: Outlook. You can open multiple mailboxes simultaneously within a single profile easily and then see mail notifications from all mailboxes simultaneously.

The pain-point is visibility.  When you switch, your other presence is effectively muted: you don't get messages, notifications, anything.  Switching has certainly sped things up ... but it's a band-aid on the root of the issue.  For consulting it's especially painful: switching accounts/orgs to focus on Client A makes you completely unreachable by Client B until one switches back.