I second the need for extending the popups when hovering over a user in Jira/Confluence. We used to have apps in this space and customers were very interested in extending those popups.
Also, will those apps extending the Teams app be able to monetize on the Atlassian Marketplace? Will those apps be coupled to Jira/Confluence/other Atlassian apps and be compatible with Cross-product-apps (which is now probably called Cross-app-apps)?