There are things in the game that tell us enemy footstep audio can work.... simply off the fact that our teammates footsteps are very loud and can tell where they are exactly even from a few hundred meters away. But an enemy 6 feet away is non-existent.
Also - after I get knocked from behind from an enemy with no sound, the minute I'm on the ground knocked... I can hear the enemy perfect! I mean I can tell if they are below me, above me, beside and even can hear the direction of their movement. To the point that I'm verbalizing to my teammate where they are and giving him an advantage. As soon as I am revive back to my feet, the enemy audio dulls to nothing or just goes away completely.
And yes, Mirage decoy footsteps are literally what all enemy footsteps should be. So it can work, these few simple examples is proof of that. So why can something not be done?
I will say this...there used to be a distinctive difference in sound between enemy and teammate footsteps despite the volume differences. But since the start of season 15, my teammates footsteps now sound the same as enemies. Not the volume, the sound. There is no way at the moment to discifer the difference between the two like in the past.
keep up the good work Respawn. : /