From the tests I've made I noticed the plugin gets loaded, even in those devices. The thing is the plugin itself decides not to proceed. So checking if it is loaded is not enough.
So you tried forcing the CKEDITOR.env.isCompatible variable to true but, as expected, it will not always work. In order to know if it will work, the best approach I can think of is to test that variable in your JS code. That means, first let the plugin load and perform whatever setup it needs. Then just:
if (!CKEDITOR.env.isCompatible) {
// Load Plan B editor
}
Note this is JS code. The quick and dirty test can be performed from chrome's console after loading the plugin, just execute CKEDITOR.env.isCompatible and the console will log the variable's value.
I haven't tested this one but I'm pretty sure it should work :)