All the code is open source, under a do-what-you-want license, including the slides, and the bulk of it is the MathBox library, designed to do exactly this sort

All the code is open source, under a do-what-you-want license, including the slides, and the bulk of it is the MathBox library, designed to do exactly this sort of thing. You are free to build upon it. If this isn't considered "accessible/shareable/tweakeable" it's because the web has regressed into a bunch of walled gardens that only serve up text and media. What isn't available is a nice visual editor or a hosting platform, but that gets us into the old code vs clicking dichotomy. I don't think I'm the right person to address that, I'm far too comfortable writing code. If I make an editor, it'll still end up a tool meant to save people like me time.