The most common feedback I get is that it seems like too much of a stretch for companies that don’t operate at Google scale. That may be true if looking at the system as a whole, but the principles behind the architecture should attract anyone’s attention - remove trust from the network by authenticating and authorizing every request based on what’s known about the user and connecting device at the time of the request.
Disclaimer: I work for ScaleFT, a provider of Zero Trust access management solutions.
Edit: If folks are interested in hearing more about how other companies can achieve something similar, here's video of a talk I gave at Heavybit a few months ago on the subject: https://www.heavybit.com/library/blog/beyondcorp-meetup-goog...