We announced at Ignite that we are actively working on bringing dynamic plus aliases to Office 365.
To get around existing usage, the plan is for an opt-in setting. Our ETA is to have this available for all customers by the third quarter of 2020.
I will keep you updated in Uservoice on our progress.
Even alerts of sign-ins from a country other than the O365 tenant's would be welcome!
This should be enabled by default. Multiple tenants only realize that their user actions were not being logged when is too late.