It appears that in order to register you extension for the HTML5 specification all you need to do is add the value for you name attribute, a brief description, and a link to the specification to this page: http://wiki.whatwg.org/wiki/MetaExtensions
I think if an entry in the above wiki was added w/ a link to http://www.opensearch.org/Specifications/OpenSearch/1.1#Response_metadata_in_HTML.2FXHTML then it may become HTML5 valid.
Would somebody in the OpenSearch community be willing to add this to that wiki page? If not I am more than happy to try and tackle it (although admittedly probably not the best candidate).
Any insight will be greatly appreciated.
Thank you,
- Jessie Keck
Stanford University