Thanks, JSC is part of Webkit so I hope it is allowed. I've emailed John Geleynse (the contact listed at the end of the WWDC talk) to get a concrete answer from Apple. It would be such a terrible waste if they disallow this.

It looks like there is a way to get the JavaScriptContext of a UIWebView using KVC, but it's not clear if that is "undocumented" and therefore private, because the whole framework is basically undocumented.