I think it'd be useful for most multilingual MediaWiki installations that use interlanguage links to have such hidden <link> elements.
Speaking of which - this reminds me of an idea I had a while ago and I was wondering if anyone would be interested to hear this. Currently many Wikipedia pages in Google search results are redirects (for example, Google for "nonogram" and look at the seventh search result). I was wondering if there is a <link> element one could use to say that another URL is the "real" page? Then the page returned for a redirect's URL would tell search engines the URL of the page it's redirecting to.
Timwi