BeyondCorp is not just a proof of concept. Everything at Google is accessed through it, including production-production (through a proxy maybe? Not sure the details). You're right about the requirement to have a hardened device -- which acts sort of like a token (as described in the BeyondCorp whitepapers). But it can be Windows, Linux, Mac, Chromebook, Android or iPhone. I never use VPN and I work on production stuff from outside the office all the time.

(FWIW, I don't think there's anything secret here. This stuff is very explicitly described in the whitepapers.)