This should make WYSISYG HTML/CSS editors possible again.

Here's a thought. Build a WYSISYG tool like that. HTML/CSS only. Round trip; that is; it reads its own HTML/CSS and works on that, rather than using some separately stored representation.

If you want to use Javascript with this, it has to be inside a manually edited IFRAME or FRAME. If you have Javascript, it's probably for interacting with a server or doing something graphical. Or, more likely, for ads, tracking, and such. Not for layout.