Kinda agree, but I'd phrase it a little differently. There exists a time element already[1]. I'd move that the browsers should allow users to change the display of this element on an element / page / session / computer basis. Often there are two or more timezones that matter for any time (e.g. event local time, user's local time, UTC). Often knowing all of these times instead of just one is useful. Rarely is just one of them at the choice of the website presenting the time useful. This is my use case, there are many more.

[1]: https://developer.mozilla.org/en-US/docs/Web/HTML/Element/ti...