It's really a pointless question.
- Take SEO as it is: marketing.
- Any SE will aim to please the masses, not the developers or website owners.
- Any SE will aim to please paying website owners, not masses.
- Today, SE will serve the HTML4 website to a user as best, and at the same time, the HTML5 website to another user as the same best.
- SE wants to take control and replace web search with their database search, i.e. give you answers not links to sites: a Googlepedia.
HTML5 is good for those that understand its benefits. Obviously, for those that don't, HTML5 keeps the HTML4 door open, in the same multiplex.
A HTML5 web document has a better granularity, which help usability and accessibility out of the box, clear element style, not pretend div.class or attribute style.
But there are no SEO implications.