Great news! We just started working on this for the AUDIO portion. We are still trying to determine feasibility for the video portion of your request.
As we announced at Microsoft Ignite 2019 this morning, we are excited to confirm that Multi-window capabilities are coming to Microsoft Teams, and will start rolling out to the public ring early next year!
Alex & the Teams team
We’re currently working on defining a compact mode experience. I will post more details when we have more to share.