"By that time surely they'll have most of the things done to satisfy the vast majority."
I doubt that. Microsoft has gotten pretty bold lately about attempting to kill off features and seeing how much people complain and if people stop caring over time. Just look at the taskbar in Windows 11. They stripped it way down, people complained, then they add back like 20% of missing features, and everybody moves on.
The new Desktop Outlook will make nobody actually happy, but it probably won't affect their bottom line either. Why would it? It's not like there is any competitor that comes to close to what Outlook does. Thunderbird? GMail? They are all worse than both the old and new Outlooks. Microsoft will simplify their development maintenance costs, make customers upset for a time, then just move on. But what won't happen is a feature complete product that anybody is really very happy with.