The advantage of LightTable's approach is that using HTML, is a simple, trivially extensible and powerful way to provide advanced UI widgeting, something modern emacs supports very poorly. Mostly due to working in a terminal if needed, but I think it holds it back a bit. The closest thing we have in emacs is pixmap support, which is poor, and painful to use!
Though, is LightTable the best/easiest way to get that? I don't know, it may be easier to render emacs buffers into a webkit view, it may also not be.