Interesting. Recently I started to learn JavaFX, partly because they might use it at my work, mostly because it looks like a good convergence of Java and graphics, so it can only interest me!

Some of your questions:
- Why did Sun not adopt Processing?
Who know? Apparently they wanted to break from Java syntax and to have native support for binding and animation.
- What's the roadmap for JavaFX licensing?
Despite some shadow corners, the JavaFX team is quite clear that, at least by using the JFX SDK, licensing of resulting programs is free, like when using Java.
- Could Processing gain by translating to JavaFX and then compiling rather than to Java?
Uh? I don't see why. Processing is very close of Java, I don't know why translating to a rather different language then back to Java would be interesting.
- What can they learn from each other?
At least in one field, the performance: they worked hard on Java to support hardware graphics acceleration, perhaps some of these would be beneficial.
On the other hand, I haven't seen yet in JavaFX any support of pixel level drawing, only vector drawing.