HTML 5 is part of the death-recipe for these native RIA technologies, but there is one other major missing piece at the moment - a fast and dependable javascript engine that can be assumed to exist on client machines.
HTML 5 just provides the UI / Drawing capabilities, but it will have to rely on Javascript perform the processing logic that is necessary in most Rich Internet Applications.
So, when it can be assumed that HTML 5 is fully implemented AND there is a fast enough Javascript engine to rival native code (similar to .NET in silverlight, actionscript in Flash, and Java in JavaFX) - then then open web will truely take over.
We're also missing an IDE as "good" (relatively) as Flash, because at the moment there's no end to end production tools that can produce the rich experiences users can expect from Flash.
Shouldn't that be "AIR" instead of Flash (that's flash+flex)?
Although HTML5 doesn't have a server-side that's necessary to compete with AIR, Silverlight and JavaFX, this gap has been filled many times by everyone. What is missing is excellent design tools - of which Adobe is the master (consider photoshop).
And so HTML 5 opens an opportunity for design tools that take advantage of it (and probably a nicely integrated suite of server tools too). Adobe surely has a project/s underway to fill it. But it's still an opportunity.
One nice thing about IT is that if you don't get in on the ground floor, you just have to wait 5-10 years to reinvent it for the next platform. In IT, everyone gets second chances (and third, fourth,...)
I'm not just being pedantic, it's that HTML5 is for the browser (not the desktop) and not particularly connected to the server-side (IIUC). However, HTML5 is competing with Flash, and the browser-based client-side aspect of the others.
But I don't claim to be an expert on HTML5, and checking http://en.wikipedia.org/wiki/Html5#New_APIs it has "Offline storage database", which is one of the key points for RIA.
That's my reasoning. Now your turn: why do you think Flash is the right competing technology?
It's too soon, but I have no doubt that JavaScript improvements and HTML 5 will completely annihilate any need of Flash &co, but it's just intuition :)
JavaFX/Silverlight/Flex are naturally converging to a browser-like structure (a DOM tree with graphical nodes), trying to emulate what the browser yet is. For technically simple - but logically intricate - application (like RIAs!) design tools will matter, not the platform itself (it remembers me how Eclipse saved Java from the decline).
I think it will take time. I'm honestly not familiar with Silverlight and JavaFX, but matching AS3's capabilities(OOP, drawing API, Loader classes, filters, tweening engines, particle systems, 3D) and the flash 9 browser plugin's penetration isn't trivial.
I'm honestly not familiar with Silverlight and JavaFX, but matching AS3's capabilities of OOP...
Um, Silverlight and JavaFX have .Net and Java inside, respectively. They don't have to work to "match" OOP, they bring pre-existing OOP to the party. With extensive general-purpose class libraries.
I don't know anything about JavaFX, but Silverlight also brings pre-existing XAML, which already has drawing and animation classes. And possibly "loader classes" and "filters", I'm not sure what you mean by those).
HTML 5 just provides the UI / Drawing capabilities, but it will have to rely on Javascript perform the processing logic that is necessary in most Rich Internet Applications.
So, when it can be assumed that HTML 5 is fully implemented AND there is a fast enough Javascript engine to rival native code (similar to .NET in silverlight, actionscript in Flash, and Java in JavaFX) - then then open web will truely take over.
And personally, I cannot wait for that day.