And lo, the committees did ask, "Shall we moveth onto feature flags with HTML5?" But browsers did speaketh in response, "Nah fam, we gud."
And now, user agent strings in Chrome are frozen, with other browsers to follow. This means they're not going to change much - it still has the major version of the browser, but all the other parts (like OS version) won't be changing. All Windows systems will be "Windows NT 10.0; Win64; x64" regardless of the actual Windows version; all Mac systems will be "Macintosh; Intel Mac OS X 10_15_7"; all Linux systems will be "X11; Linux x86_64" and all Android systems will be "Android 10". https://www.chromium.org/updates/ua-reduction/
AFAIK the aim is to totally remove user-agent one day, and instead migrate to the newer Client Hints API.
That was a fun ride!