Wow, this is really beautiful. One thing I feel lets it down is that "text-align: justify" still isn't on par with print quality in browsers. It is getting better, but it's still a way behind pdflatex+microtype.
I'm sure there's work being done by talented people, but it's a hard problem, and maybe there's been compromise between speed and quality stuck?
My understanding is that the main problem is incompatibilities between the CSS and TeX layout models. That's not to say that there isn't still plenty of room for improvement, however.
I'm sure there's work being done by talented people, but it's a hard problem, and maybe there's been compromise between speed and quality stuck?