Very interesting! Could you drop a line on the github repo how to use the phonegap build process with an app build for node-webkit? this would be awesome! I'll not have the time to make your described wonder happen, but at least truly crosscompiling apps for desktop & mobile is a thing I'd like to see happen.
the easiest way is to use build.phonegap.com and connect it to your github.com repo, as well as your src directory in the grunt build tool.
Cordova is the open source project uses the same code magic that phonegap does, and can be installed on your local machine. I have not mixed it into the grunt built tool yet, but I think the hardest part is installing cordova & ready the documentation
