Sorry, there seems to be a disconnect here. Yes the difference between back stage and front stage is a gray-scale. However that was not my point: Making selfies is an act of front stage, not because there might be other people around, but by the mere fact you are making a photo of yourself with the purpose of it being seen by others. The performance is that what we see on the photo, not the conditions it is made under.

The conditions it is under might make it into more of a front stage, but given that the selfie itself is front stage the fact that you are not hiding making it is very hard to see as "authentic" back stage behavior.

People might use selfies to practice (back stage behavior), but you will normally never see those and what they do present is obviously fit for front stage.

Yes you might walk into someone practicing with selfies, or accidentally see some practice selfies, but that in itself does not provide better or more reliable information than any other incidental back stage information like seeing someone in the shower.

Now if your point was that selfies invite us to perform too much and practice too little than we are in agreement.