It would be awesome if there was an ArcGIS for Teams option when adding a tab in a Channel. For example, if we have some useful applications/maps that we'd like to have readily available for the team beyond simply pinning:

There is a workaround if you use the Website tab and enter the URL:

But the non-GIS users and users that don't know the URL want to simply search for content within the organization, and an ArcGIS for Teams tab that did that work for you would be best.