New, or legacy? Maybe both?

Nota bene, it's not an avant-garde idea by any means - but I truly believe a site should be usable from any browser. Sure, you can pioneer the use of a new JavaScript api, but contrarily it should still have some form-based fallback for people who can't use that standard; this may sound like basic backwards compatibility - but it's not. Whether the user is using the latest nightly release that fully supports async functions, webgpu, and web-assembly - or a decade old PS3, iPod touch, or even a antiquated text-only browser it should still WORK, you may not implement all the niceties the core functions, navigation, and general usability of your site should stay intact with forms, hyperlinks, or heck - even applets if it comes to it.