I can't help but wonder if this HTML-based setup is actually more trouble than it's worth. It seems there's a very complex ecosystem in there that is hard to reason about in this way, and it's a top-level requirement for a browser to sandbox the various bits of code being executed from a web page.

Obviously hard to say what those tradeoffs are worth, but I'd be a bit nervous about it. The work covered by this post is a good thing, of course!