What to learn for RIA
You should focus on “HTML5” where “HTML5” is the new “Ajax” buzzword aka. the “Open Web Platform”—not just the HTML 5 spec itself.
Flash, Silverlight and JavaFX are all single-vendor plug-in offerings but “HTML5” is a multi-vendor browser-native thing.
If you want to an IDE workflow, you can use the Google Web Toolkit to have a Java workflow that targets the browser-native plug-inless feature set. Unfortunately, there’s no GWT-like Python system yet.
I am planning to build a RIA about a year from now (when my current contract ends). What technology would you recommend investing time in? 
I will need good cross browser/platform support for video, music, and canvas.
And ideally I would like to leverage my Python skills.
Silverlight looks interesting because I could use Python through .NET. But I'm on Linux so I'd always be a 2nd class citizen. And it has a low install base.
Flash on the other hand has a large install base.
And I'm not sure about JavaFX because of the Oracle deal.
Or should I hold my hopes out for HTML 5?
Thanks!