To end this a bit OT dicsussion, just a last statement.
The MAC must be unique inside a network segment where only level 2 traffic exists.
As an example take your post address.
It consists of your town, street, house number, name.
Inside your house your name should be unique.
Inside your street your house number should be unique.
inside your town the street name should be unique.
To make the city name unique mostly postcodes are used.
Uniqueness inside one system doesn’t demand global uniqueness. This was the idea with the definition of MACs ( global uniqueness give local uniqueness automatically ).
The idea of changing the MAC on smartphones doesn’t really hurt local uniqueness, because each network ( identified by 802.11 means ) gets its own unique MAC which is repeatedly used for this network.