Great, thanks Lesley. If it is mainly SEO then it's not a major concern for me right now. We currently rank well anyway due to age and authority (I presume - who knows the full reasons...) and I can always add html5 tags like header, article, section etc when I create a child theme which is what I presume you are referring to?
I'm also optimistic more theme/mod developers will start native support soon.
Personally I'm very excited about this project and look forward to seeing it grow and maybe, if time permits, helping out in a small way.