As you may already know, Exchange (both on-prem 2016 and online) supports the use of OneDrive for Business for file storage (including attaching files from OneDrive for Business).
An update is going to be deployed (as usual Targeted tenant first with a completion scheduled for end of September) to allow use of third party storage.
IMPORTANT NOTE this updated feature is not enabled by default; which means if you want to enable it you will need to connecting to your Exchange Online with PowerShell and run the following command
Set-OwaMailboxPolicy –ThirdPartyAttachmentsEnabled $true
Great feature but what about supporting SharePoint Online by default and not just OneDrive and Groups.