HTML5 and CSS3 compliancy for general
I believe this approach gives more freedom to the template developer http://ideas.joomla.org/forums/84261-joomla-idea-pool/suggestions/2277030-html5-support-via-xml-switch-in-joomla-template - Joomla! just makes sure it converts anything it outputs in <jdoc:include type="head" /> to the HTML5 equivalent. Easiest way to implement HTML5 in Joomla! now, not in 2 years...
James Durrant commented
Mathias Roth commented
insert <menu> <article> <figure> etc.-tags as these are the new standards and will provide many new features for template design and SEO. Also the use of Microformats and XFN-tags should be supported in WYSWYG-edit