Not just an interpreter – unless there's a standardized subset that one can look for as a web developer then one can't really adopt to it (through either graceful degradation or progressive enhancement). Same reason why eg. Noscript addons creates havoc at times. Web sites expects a certain baseline and when it's not there, they expect that javascript will be disabled altogether and <noscript>-tags to get executed, but just disabling some code prohibits that fallback, making it less usable than fully disabling js.

Good point. I guess there's no real hope, then. I'll take the runner-up position in that case -- I want a browser that has no support for Javascript and the like at all. In the meantime, I'll just continue to leave it disabled.

Closest I can think of is efforts like https://jerryscript.net/ and https://duktape.org/ – but the challenge isn't in the language itself really, but in the web API:s that gets added to it.

Eg. Node.js doesn't have WebUSB either :)