Native.js is interesting. I would wonder how it plans to handle things like callbacks for various events though. As an example, a keypress in a textbox (e.g. pterosaur). I haven't looked at the WebExtensions API in detail yet, so it may already be a solved problem.

More specifically, editing text seems oddly neglected, which is disappointing considering webmail, blogs, social media, stack overflow, etc... I'm glad noscript is being given special consideration.