Modern Auth and Unattended Scripts in Exchange Online PowerShell V2

Extremely slow connection times using OAuth2 makes my app almost impossible to use.

Ok I have now (finally) been able to convert a web application which is used for managing Office 365 mailboxes and their settings from Basic auth to OAuth2 using certificate thumbprint.  However the response times are terrible. 

• Connections which previously took under 2 seconds now consistently take between 12 and 20 seconds each. 
• Because this app needs to run multiple sequentially called cmdlets in o365 to get the required data or to write the required changes, this added delay is compounded. 
• A page load which previously gathered all info using calls to get-mailbox, get-mailboxpermission, Get-RecipientPermission & get-user which previously loaded in under 30 seconds (just acceptable) now takes almost 5 minutes. 

As we hurtle towards a basic-auth shut-down date (apparently only a handful of months away) I am desperate for a solution for this.  This is an enterprise wide app which is used by 35,000 staff globally and the new slow experience makes it almost impossible to use for most functions. 

I have heard that the Graph API is supposedly being extended to allow several basic mailbox cmdlet-type actions which may or may not be what we need(?), and is assumed(?) will have much faster response times, but nobody seems to know anything much about that.

• Does anyone know what can be done to reduce the connection time for OAuth2 using cert thumbprint to somewhere near what it was for basic auth?
• Does anyone have a time-line for the new Graph API functionality and what capabilities it will have?

Given the fact that shut down date is getting close and if either of the above 2 possible solutions actually materialize, we will need significant development and test time.  Is there a plan to extend the cut-off date further, given the slow delivery of workable solutions?