Apple SVP Federighi: Touch ID was not intended for multiple users20
While there are some Apple iPhone X users who would have preferred Apple to offer Face ID support for multiple users (such as the husband and wife that trust each other so much, they each allow the other to register their fingerprint on the other's iPhone), this is not in the cards for the foreseeable future. According to a reddit post made by Apple's senior vice president of Software Engineering Craig Federighi, Apple continues to focus on Face ID as a single user authentication system.
Interestingly, the executive stated that Touch ID was also designed to be used by only one person, who would register the finger and thumb on both hands. The design also happens to allow multiple users to sign-in using their individual fingerprints on the same device. If Federighi is right (and he should know), nothing similar will be available for Face ID, at least for a few years.
source: reddit via BGR