Audible/Tactile Cues for Guardian System

I work with a team that uses the Unity SDK to create serious games for VR. I really like how the Guardian System is set up but I have one suggestion on how to improve it as far as accessibility. At the moment I've only noticed a visual cue for when players are about to leave the play area, but in some of our games we have had users accidentally back or side-step because they don't see it until it's too late. Perhaps we could have a standardized system for generating an inobtrusive audible cue and/or handheld vibration for when a headset or controller is approaching the boundaries? While I intend to include this sort of feature in my products, it seems like something most games would benefit from, and that the user might want to be able to customize for use in all software.

My apologies if I've overlooked it and this sort of feature is already implemented.