As far as I can see, this is probably one of the nicest things to ever hit web design: http://www.w3.org/TR/css3-grid-layout/. It will allow for complete separation of content and layout, without the need for all the float/margin crazyness that currently makes CSS layouts such a pain. It makes any kind of layout, including 12-column-grid-with-gutter layouts incredibly easy, with no manual calculation required (grid-column-span etc.). Also, it's just logically really nice.
Obviously it is not widely supported by browsers yet (http://caniuse.com/#search=grid%20layout), but a prefixed version will be available in IE 10 . Issues are open for other major rendering engines: https://bugzilla.mozilla.org/show_bug.cgi?id=616605 and https://bugs.webkit.org/show_bug.cgi?id=60731
I would like to think that by providing a good layout.css for zen, we might stimulate the two leading FOSS rendering engines to pick this up a bit quicker.
Obviously this isn't super high priority at the moment, but it'd be awesome to the the web's most popular CMS' most popular theme implement this, if only as a proof of concept, so I thought I'd throw the discussion open.