Looks really interesting - using C++ for the main "business logic" and linking into Java or Objective-C for UI stuff, thereby keeping the main codebase cross-platform and keeping a thin UI layer for the different platforms.
I guess this is good for projects where native UI is important. They seem to link into their own "record" data structure, translating equivalent types across languages.
Really interesting part for me is that you can seamlessly call Java / Objective-C from C++ as well the other way around (I've been having a tough time integrating an Objective-C library into my C++ code...)
I wonder if any of this could feed into JUCE somehow, to allow easier integration of external platform-specific libraries or to make calls to the native UI, translating JUCE types e.g. String and Array into their Java or Objective-C equivalents.