O365 Webhook Subscriptions for All Users Calendars

Question

There is an existing question which already has an answer; however, the answer comes from a Microsoft developer and reads, "We are working to support the scenario you are requesting..." and goes on to provide a method which doesn't seem to answer my question.

Original article: Using Microsoft graph to read all users calendars

My question is, rather than subscribing to a single user's mailbox or calendar, is it possible to subscribe to all mailboxes or calendars?

My application needs to listen to the create/update/delete events of calendar meetings and insert them into a SharePoint list.

POST https://graph.microsoft.com/v1.0/subscriptions
Content-type: application/json

{
   "changeType": "created,updated",
   "notificationUrl": "https://webhook.azurewebsites.net/api/send/myNotifyClient",
   "resource": "me/mailFolders('Inbox')/messages",
   "expirationDateTime":"2016-11-20T18:23:45.9356913Z",
   "clientState": "subscription-identifier"
}

References:

1. Using Microsoft graph to read all users calendars

2. Creating a subscription - https://developer.microsoft.com/en-us/graph/docs/api-reference/v1.0/api/subscription_post_subscriptions