I was just approached by a colleague of mine having performance issues, while connecting to Exchange Online using the new EXO V2 module using app-only authentication.
The behavior lead into an overall elapsed timespan of over one minute, until the connection was finally established!
I know that this topic is really a topic with gets high attention.At the moment there is nothing available in Microsoft Graph, which would make it possible to manage objects in Exchange Online.
The few things, which exists, are more for end-user (e.g.: accessing their e-mails, calendar or tasks) and for auditing and reporting (e.g.: Security API). Nothing available for managing a mailbox permissions or attributes. Not even like simple CustomAttribute1-15.
Now Microsoft released a new Exchange Online PowerShell module: EXOv2.