It is impossible to say how soon this system will appear in serial products and whether it will happen at all.
Apple has filed a patent application that describes a protection system for smart glasses. It provides two modes of operation of the optical system. One is working, the second is protection mode.
In the operating mode, the lenses of the optical system projecting the screen image into the user’s eyes can be very close to the screen. If the device falls, the result may be a hit of the lens on the screen and damage.
According to the inventors, if the motion sensor detects that the glasses are in “free fall”, the optical system should automatically go into protection mode. In this mode, the actuator pushes away the optical system and, as an option, fills the space between it and the screen with air, liquid or a soft separator to further soften the shock.
Among the possible liquids urgently filling the space between the optical system and the screen, ferrofluid is named (a suspension of ferromagnetic particles in a liquid carrier, strongly polarized under the influence of a magnetic field).
It is impossible to say how soon the described development will appear in serial products and whether this will happen at all, since we are talking only about the patent application.