This feature request is working its way through the backlog queue. No new details are available yet.
We have deployed and adopted SharePoint Online and Team Sites, and have built out project management support sites for governance and auditability according to our project management framework globally. We cannot effectively use Teams without being able to link them to existing SharePoint sites. We will have mass confusion with our project team members on where to store project deliverables, etc. This will likely result in an audit finding if we're unable to track all project collateral in the designated and approved site.