Send an email to all their users, and not the 0.001% who use this feature?

The users of this feature, of course.

But that would require the dreaded telemetry, which that subset of users care deeply about not having and would cry fowl if it even existed.

"Why the hell are you collecting information about what file system types I privately run OneDrive on M$!!"

Why, indeed.

Yeah it's impossible to get reliable statistics without using sleazy tactics to force every single one of your users into your spying 'telemetry' oh wait it isn't. Microsoft has a bazillion customers, their statistics will be fine if 99% of all users disable their spyware.

As far as I can tell, Microsoft told nobody. A blog post and an email to OneDrive users would have sufficed, neither of which use telemetry or happened.

Oof, no telemetry please. They know I'm a subscriber and have my email address.

This makes me wonder, do they have data on how many users are saving onedrive files on FAT? Is that info they could pull? I don't see why not...

That'll be Windows Telemetry story all over again: lots of people opting out or complaining everywhere they can.

They wouldn't need telemetry - they could have shown a local warning when the OD client detected a FAT drive.

And people whining about people whining. Reality is that they do force telemetry, people aren't opting out because they can't and they are complaining amongst themselves because Microsoft doesn't care.