How to use WordPress 3.5 media manager gallery tool for my own plugin
You can call a = wp.media.gallery.edit('[gallery ids="2,1,3..."]'); like Wordpress does in media-editor.js.
I wasn't sure what event can catch the update, I found it with a.on('all',function(n,a) {console.log(n); console.log(a)})
Notice "update" in the log, and an object with a models array with the images. So, the quickest solutions using the gallery selector would be:
wp.media.gallery.edit('[gallery ids="numberlist"]').on('update',function(obj) { do something with obj.models)})