The catch, if there is one, appears to be the hardware. In a video (embedded below) Microsoft notes that Hello will require “specialized hardware, including [a] fingerprint reader, illuminated IR sensor or other biometric sensors.” That would imply that the laptop would need a built-in Kinect-like sensor, either one designed by Microsoft—such as Kinect for Windows—or a RealSense sensor from Intel. (Microsoft said that all PCs incorporating the Intel F200 RealSense 3D Camera will support the facial and iris unlock features of Windows Hello, including the automatic sign-in to Windows, as well as unlocking “Passport” without the need for a PIN.)
A Microsoft spokeswoman also confirmed that Hello will not work with an ordinary Webcam.