On profiling American Sniper, I've noticed that there is a new/newish Dolby sound recording system: 'Dolby Atmos'. It doesn't list this with any channels ( 2.1, 3.1, 5.1, etc.,) so will this be appearing in the Audio drop-down list?

You state that it is newer than the latest update to come out, Dolby Atmos first appeared when Pixar's 'Brave' was released in 2012. The home version started to appear in the mainstream Bluray releases sometime in 2014, so really it is not newer than the latest update, though more and more blurays are being issued with it. For the home cinema aficionados, it will be a more immersive and 'atmospheric' experience, with different placings of speakers in the room. In the meantime, as you say, wait until the programme is updated.

While we wait, you can create a tag "Dolby Atmos", then when it's available you can find your Atmos tag and add the sound track to the profiles.