Doing it inside a custom element like <py-script>…</py-script> has been done occasionally, but doesn’t work well because (a) the code is now visible in the document by default and only hidden by stylesheets, and (b) < and & now need to be escaped as < and &.
This is something I find common in the Python ecosystem. There seem to be a lot of choices made more for the benefit of the developers than the end users. Even getting a Python app with some idiosyncratic build system to run can be a challenge sometimes.
Lua in the browser: https://fengari.io/
And then you can use that to run Fennel, a Lisp that compiles to Lua https://fennel-lang.org/
I think TypeScript also has a script you can include that lets you put your TS code in a special script tag, and it gets compiled in-browser.
That you have to ship the entire interpreter isn't great, but what it means for development is that there is no compilation step. You don't have to deal with the WASM toolchain directly. You write your Python code, refresh the tab, and see the results. That's a huge step up from trying to use Rust and WASM for the majority of people who aren't yet Rust developers.
Obviously it's super immature at this stage, but the future possibilities are exciting.