Man, I hate being right when it comes to things like this.
"We strongly believe Office 365 delivers the best and most cost-effective experience to our customers, but we understand that some customers have reasons to remain on-premises."
I said it way back in 2015 and had a conversation with some random Microsoft employee about how Exchange is going to be an on-premise product for a log time to come. I strongly disagreed with this guy and when I can remember some key words from that discussion, I'll follow up to this post in order to make him eat those words. Microsoft just moved Office to an online-only distribution model so the next step won't even be noticed by people. Exchange is next. They've been forcing us to the "cloud" for years and Exchange is dying a slow death. When they finally stop releasing new on-premise versions I'll keep using old ones as long as I can because I, and the customers I support, will NEVER move our messaging infrastructure to the cloud.
It's not just going to happen, it's currently happning, right now. Farewell.