Techniques that require a plug-in in the browser are dying. However Silverlight is not the one dying, since it was already dead just before it started (why even try to penetrate a market with a product that is not finished and with a competitor that is 4 blocks ahead). Therefore we can conclude that Flash will disappear, AIR will disappear and finally those ugly Java applets (who ever thought those would be useful on the web, waiting 5 minutes to have an applet loaded) are gone too.
Native wins
For me it is clear that all plug-in based techniques will be replaced by more native techniques like JavaScript. JavaScript was forgotten due to some browser wars which ended up in the result with two rather incompatible implementations of JavaScript. However with the several incompatible implementations becoming less dominant (there now is only one implementation that is questionable at some points) and the rise of the libraries like JQuery, Prototype, SproutCore, YUI, MooTools, ExtJS it is clear that JavaScript is back on its feet again and it is running to overtake all these plug-in based techniques. JavaScript is platform independent, as most plug-in based techniques are not.
The limitation in JavaScript used to be the ‘flashy’ things: drop and drag, animations, interoperability and other nice and fancy stuff that was either limited by the technique or by the processing power of the client. Nowadays this isn’t a limitation anymore, do you want nice animations, you could use script.aculo.us, JQuery UI, or Processing.js. Interoperability is arranged in almost all libraries. Do you want applications that feel like desktop application, think of your design and build it, just like 280 Slides, Google Docs, Zoho and SproutCore gallery. You are no longer limited, you can make these things happen with techniques that are native for all browsers: HTML, CSS and JavaScript!
No vendor lock-in
It will be hot JavaScript winter, especially since everything is possible again. Flash, AIR and Silverlight aren’t the only techniques that can make flasy desktop like nice solutions. JavaScript can do that too and JavaScript does not create a vendor lock-in requiring a specific closed source plug-in.