This app was mentioned in 3 comments, with an average of 1.67 upvotes
The best workaround I've found is to use Go Show or Go Show Free as it let's you view anything on your YouTube watch later list and has a 360 view option. It works great for me on my MotoG. Hopefully official support will be available soon.
It has to be supported by the app, but I know GoShow and Cmoar Virtual Cinema both support 2d because I have those.
Hey, if you happen to have a Google Cardboard and want to watch it in VR, there's an easy way to do so! All you need to do is download the video (you can probably find something that works out there, it downloads like every other video out there) and open it with a 360 video viewer ( I recommend Go Show, but if you don't want to pay there are plenty of other options.
It's not 3D, but it works!