It's frustrating how we're still fighting over this stuff when 99% of documents and spreadsheets (the data, not the formulas) could be zipped html except if not that spreadsheet editors and document editors don't have a standardized subset of html to support.
ODF is just XML.
That sounds rather bad idea. HTML is really not designed for proper data storage. It can display something, but I don't think it is right tool for the job. Just because html can present something like tables doesn't mean it is right tool for tabular data.