At 48 bits, this would seem reasonably safe: you would need 751 devices on a network to have a 1/1 billion probability of a collision, and 751 devices with entirely layer 2 connections are rare -- usually there is a layer 3 router in between somewhere. And a switch whose CAM table is limited to 25000 entries would not support more than a 1/1 million probability of collision, if it were ever used close to capacity.
What are the motivations behind the current scheme of MAC address administration that address a concern not solved by random MAC addresses?
8 5 5 5 6 5 7
is as just random as the sequence1 2 9 5 6 3 8
. What I wanted to say is, that "unique with great certainty" is not "unique", you have a great certainty that it will not collide...but it is not guaranteed. Many people get this wrong and their systems fail afterwards because they did not take collisions into account.