Subaru's top rated (iihs.org) system which uses stereoscopic cameras seems to be a proven better, simpler system. That Tesla is going to stereoscopic cameras would confirm it. As noted above, in practice, it is a very sophisticated and effective system.
The Subaru got the top rating because it was the only vehicle that came to a complete stop in a 25mph test collision avoidance test (I should note IIHS did not test any Tesla vehicles yet, so we don't know how it compares in the same test). It is not necessarily because of the superiority of stereoscopic cameras (the logic and rear end collision risk that an automaker programmed into the system can have a lot to do with it).
Also, I should dispel the misconception that the two cameras that Tesla might release has to do with a stereoscopic system.
Just to make people aware. Subaru's Eyesight system uses two cameras mounted
14 inches apart and has no front radar backup to confirm distance to objects in the front (the latest vehicles have side and rear radar for other systems, but still no front radar). Stereo systems rely on something called disparity mapping to generate a 3D depth map. It can't function properly even if only one of the cameras are blocked or misaligned.
Embedded Vision: Detect Pedestrians | EE Times
See how far the cameras are mounted from each other in the Subaru system:
Subaru Forester review: The best small SUV thanks to EyeSight | ExtremeTech
The Model X housing however has a camera housing that allows a distance of only around
3 inches apart for two cameras (I did a rough estimate using the Model X photo on the Tesla website):
This is presumably to support the Mobileye EyeQ4 system (or something similar given recent announcement of the end of the partnership) which despite supporting up to three cameras,
does not use the cameras for stereoscopic depth sensing purposes. Such a short distance between the cameras would make stereoscopic based depth sensing poor esp. for the long range.
Rather the multiple cameras is used to support
different field of views, suitable for objects/pedestrians both in normal (50 degree as in the current single camera), close (pedestrians in the city), and far range (past the 100-200 meters of today's system). Here's an article that describes this and an illustration that shows how the three different cameras would be used:
The Linley Group
In practice the range seems to be close to 300 feet when it first detects objects and gives audible warning. It will then pull within range (four different following distance settings) and start to slow.
Even the oldest version of the single camera Mobileye system can do vehicle detection out to 70 meters (230 feet) and 100 meters (328 feet) for version 2 using a cheap VGA camera. If using a higher resolution camera, that extends to 200 meters (656 feet). Tesla currently uses version 3 (which I presume may have even longer range).
Vehicle Detection - Mobileye