About twenty-eight months ago I looked into ruby in HTML. Earlier today ruby support was added to HTML5. (The sole browser to support this remains Internet Explorer though, unfortunately.)
It would be really cool if people who use ruby already could take a look and provide feedback (public-html-comments@w3.org, whatwg@whatwg.org, or below). Thanks and all!
It looks like Mozilla plans to finally implement ruby-support for Gecko 2.0. However, it will be a long time before this will reach end users.
Anyway, if Mozilla starts, maybe Opera and WebKit will follow, and maybe someday Internet Explorer will get complete support as well.