Is it possible, or will it be possible, to stream live in 3D?

It would certainly be possible to create your own stream using the old fashioned red and blue method. You can then load that, alongside a normal channel without the 3D, in a package to provide users a way to watch both.

That said, there is no built-in way to transfer a stream to be viewed over 3D or anything that doesn’t require work on your part.