I was able to test this on Windows phone is August and then again on Android in October but then it vanished. Voice authenticated User accounts would be great for different cortana devices for a family that use one centerally located invoke or echo or the xbox or a community pc. Please get this done.
@LeonidasSpartan2 So far as i can tell you can use multi users. in cortana settings you can train her to respond to only your voice or you can set her to respond when anyone command her. this is done via the device she is connected to. i hope this helps you.