Then Windows could pull a ChromeOS. The only place where a native UI is really needed is the lock / login screen; a tiny subset of any current UI toolkit would suffice.
Office on Windows relies heavily on COM and other Win32-only libraries to function.
I can't think of a valid reason to rewrite Office to that extent. They already have Office for the web and Mac Office; while not identical in features, they're often good enough outside of BI scenarios or highly complex Excel work.
Outlook is the lone exception where that team decided to have Outlook for the web, Windows Outlook, and Mac Outlook be identical, so those are getting their rewrites with removal of Win32-specific features where applicable.
See BUILD recordings from 2018, I think, where they demo the new UWP controls contributed by the team, similarly to what happened before with the ribbon on Windows 7.
I would vouch they got as happy as the rest of us.
I wish they didn't. Outlook on macOS is abysmal nowadays and I still find myself resorting to the legacy view just to change some settings that both iterations can read but only one exposes.
I significantly prefer using Thunderbird or the web views for Gmail and Zoho Mail over any version of Outlook. Is the integration across O365 apps nice? Sure, but the platforms themselves are miserable to use.
In a similar vein, I was cautiously optimistic about Teams V2 for unifying the client. But then they completely dropped the Linux client for their PWA which does not have feature parity with the "native" platforms and has a significantly worse UX.
I used Thunderbird for years, mostly to keep my NNTP feeds going, at some point, my mailboxes corrupted between versions (the NNTP site I was using didn't work right anymore) and I just kind of gave up at that point. It was in the dark time, before the more recent resurgence of dev activity, but NNTP didn't seem to be even a tangential focus.
I'd love to see a relatively easy open-source server for mail+contacts+calender that allowed the level of visibility, management and sharing that Outlook+Exchange/o365 offers. Right now, I have some of that, but not nearly the same.
Edit: Also, really sick of getting meeting change notifications in Teams for a meeting that is months away... just leave any meeting notifications beyond today/tomorrow in outlook, I don't need them in my workgroup app.