> To be precise, XHTML promised that pages render faster, which turned out to be browsers fault, not markup.

I'm not sure XHTML ever promised faster rendering, I'm sure many people (including me) _assumed_ it would render faster. The truth is that XHTML rendered considerably more slowly! This days XML parsers have improved, but for a long time XHTML made partial rendering while loading and other things harder which meant loading an XHTML page took much longer than the plain-old HTML version.

I doubt rendering XHTML will ever be faster, at best it is/will-be not measurably slower than HTML.