Is it fair to say the development of HTML5 has been somewhat stagnant? That mostly depends on your perspective and occupation I suppose. At the moment, new HTML5 features are being release that might seem impressive to the untrained eye. However, Adobe’s Flash application was doing the same neat tricks over five years ago. Since we are on the subject, it is also fair to point out that most older browsers do not support HTML5, but support Flash. (via plugin download).
I, for one seem to be stuck between a rock and a hard place. I detest writing extra code for older browser support, but will gladly do it for the client. I will never go back to using Flash under any circumstances and have made it a point not to even have the application on my system. However, I hate the fact that I once had format videos for .MP4, OGV and WEBM so the new HTML5 video tag can work. With Flash, all I had to do was upload an .MP4 video to the flash player and I was done. Most importantly, it worked on all browsers. Some of the other issues I have struggled with are not actually HTML5 problems, but many will group it all under the same umbrella. Vendor prefixes are a pain in the ass. The fact that you have to download, buy or jump through hoops for some plugin to resolve this issue brings me no joy.
In spite of all my grieving, I am sort of like an advocate for HTML5. I still believe it is a very good thing for the web and makes way more sense than just using a multitude of div tags to structure a page. I only use a handful of HTML5 tags myself to avoid complications, and to be semantically correct. I am not sure what the future of this Markup holds, but whatever happens, I want to exterminate all ancient browsers and do away with all vendor prefixes.