Teams deployment with on-prem mailbox

Hi,

What do you think would be the major disadvantages for a tenant who already has an Exchange Hybrid setup should they decide to roll-out an upgrade from Office 2016 to Office O365, and deploy Teams and OneDrive, and delaying the mailbox migration to a later stage?

I'll kick off the list with a couple of thoughts of my own, but can you please challenge my assumptions and/or add to this list?

The risk of unknown unknows

If/when there are any challenges with the configuration of Outlook, Outlook Mobile App + Intune,, or with any Exchange configuration, support will be harder and more limited as new features are thoroughly tested by millions of EXO users, but the user base of orgs with mailboxes on-prem is getting smaller every day.

Less Signals in the Graph

If the mailboxes are on-prem, mail signals are not entirely available for Graph analysis (Is this a correct assumption?)

As a result, Viva Insight productivity suggestions and wellness nudges won't be available. ( not available at all, or maybe just limited in their smarts?)

Also, from a security perspective, without the mailbox content to process, how would this affect the understanding of standard vs. risky behavior or the effectiveness of other security controls like DLP, rules based content classifiers, or the tagging of emails with data sensitivity labels?

Opportunity Loss / crippling adoption

Power Automate flows wont be able to email you, and you can't trigger flows from on-prem shared mailboxes

You won't get task reminders and other notifications from any process that relies on Power Automate

The feature crippling in Teams, can be enough to put users off the platform and irreparably damage the platform's reputation (Or am I being overly dramatic here?)

Thanks for reading. Looking forward to hearing your thoughts!