I once implemented a knuth style renderer to properly typeset books into html. IMHO If you want to do advanced typography you need to algorithmically set the width and offsets of spans and use spacer elements. Otherwise all that complexity has to go into the css spec and that will be a lot for what is otherwise a niche use-case. Another problem is that good typography is algorithmically expensive and is best computed ahead of time, rather than on page load.