Even if HTML5 becomes a viable Flash competitor technically, it will take one heck of a good, free, multi-platform, point-and-click development application for it to compete with Flash already coming right along with Photoshop and Illustrator in Adobe's product suites.
Well, given what's been demonstrated here, I'd not say that such a development hurdle is that far away (developer also points to a WordPress implementation of feature/coding; showing its possible to package this methodology into developer-centric solutions such as templates or snippets relatively easily). The challenge is the politics/economies, and that part Flash has a win with - for now.
On Flash: after that post on the Flash blog was shown that only two of the sites in question were wholly dependent on Flash I'm surprised anyone "in the know" is still making the "what will replace flash" argument. CNN, NYT, Youtube and the now infamous Bang Bros sites all accessible without flash. Hulu has dumb execs who tried to block Boxee because of some nebulous threat to it's bottom line will try to hold out. but when millions of their customers are on devices that cannot access their website lets see what they do.