This is an excellent step forward in the effort to protect sensitive Google data. U2F is a strong, reliable authentication mechanism and will afford Google more flexibility as this program moves forward. There are certain limitations with mobile devices and third party applications that will need to be navigated, but if someone finds him or her self in a highly sensitive or high-risk situation, then this is the best security option available to date for the Google email ecosystem.
This is an interesting read. It is always exciting to see multi-factor authentication grow and evolve. U2F is a promising direction in IT security.