You could write a standard.

If it actually gets mainstream adoption or goes into the standards pile it another question entirely.

If you can convince Apple, Google, and Microsoft to implement your standard: sure. Attempts have been made with varying success.

Your standard still needs to render in Outlook on Windows, though, which means you need to support the weird Office version of IE11 as an upper limit.

Does the email client on Windows still use IE11? (Some older versions might still have significant market share, but I’m not sure it would be for much longer?)

"Outlook (New)" (aka "One Outlook") is React Native with a full Chromium webview, and the transition from out-of-the-box Windows-provided "Outlook Mobile" (Windows 8-10) to "Outlook (New)" has mostly completed, but the transition from Outlook (Classic) (aka "Bloated Corporate Outlook") seems somewhat stalled because a few big corporations have extensive plugins and cranky IT admins. (Also Outlook Mobile had a better than IE11 support and also has been Chromium on most platforms, it is "Outlook (Classic)" that continues to haunt us all with its ancient Word-based micro-browser fork of IE.)

Sometimes I really wish MSFT broke backwards compatibility in the places that matter, not places their corporate customers don’t care about.

Google has recently been pivoting AMP which nearly broke the web towards email. It might actually be a better use of AMP than the web, but I'm still skeptical about some of its privacy stance and ad-injection focus: https://amp.dev/about/email