4.3 feels more like 4.2.3
Android 4.0 (Ice Cream Sandwich) was a huge step up over the earlier Android builds. After that, it's been baby steps, but Google have at least been consistently making that progress. For example, The latest Android adds the SELinux kernel below everything else. Supposedly, the fancy security features are turned off, because they don't want to break anything. Yet. But they're there and people can start playing with them.
Is there any possibility that Chromecasting could be opened up for cross-platform support?
Supposedly there will be a SDK. I'll be curious to understand how it works. I'm particularly curious how they worked out the security aspect of it, since its Google TV / YouTube predecessor has no security at all. If you're on the same network as a Google TV, your phone magically sees it and can send video to it. There's no pairing, no passwords, nothing.