I haven't seen an official statement but see the following from https://www.macworld.com/article/3225406/iphone-ipad/face-id-iphone-x-faq.html
For now, an iPhone X will recognize only a single face. That could change in the future. But you can no longer give a spouse, partner, or other person access to your phone through a biometric means, like you could by enrolling one of their fingers with Touch ID. You’ll need to share a password with them.
According to a MacRumors report, an email from Apple VP Craig Federighi to a customer states that Touch ID was intended for a single user only, not for multiple users.