This is great news and very welcome.
At the same time there is a lot to unpick, especially in desktop app. I have made a lot of use of account switching in the desk top apps. It is a wonderful time saver and helps me stay organised. But it hasn't 'trickled down' into every nook and cranny. For instance, I live in Outlook desktop and have accounts for my business, my personal life and two clients. My clients want me to use their branding, but Outlook doesn't let me set a theme per account - unless I switch. That would mean constantly switching between 365 accounts to send emails that are 'on brand'.
It would be great to see MS collect these more detailed requirements and make the Office Suite even more powerful in the modern world.