It is not default offline at all. http://www.youtubego.com/signup/ http://www.youtubego.com/signup/ From the screenshots, it looks to be trivial functionality

It is not default offline at all. http://www.youtubego.com/signup/ http://www.youtubego.com/signup/ From the screenshots, it looks to be trivial functionality that could be baked into the existing app. Besides the ability to download and play files is not something I consider to be a "HUGE" architectural change.