Gmail warned us that a more restrictive DMARC policy was coming, didn't they? That warning came all the way back in 2015. They said that "p=reject" was coming. Maybe it still is -- we're not there yet, but this appears to be a step in the right direction.
Today's update: For subdomains under gmail.com and googlemail.com, they've implemented a "quarantine" DMARC policy.
They're not the first to implement a DMARC "quarantine" policy for some part of their domain. Apple did the same thing back in July. Mail.ru went to "p=reject" back in March. And of course OATH (AOL and Yahoo) started this trend, implementing a "p=reject" policy for their main domains way back in 2014.
Edit: Ha ha, fingers sometimes move faster than brain. To clarify, this applies to subdomains of gmail.com -- i.e. bounces.gmail.com, server.gmail.com, etc. The DMARC policy for the top level of gmail.com and googlemail.com is still p=none. My bad for suggesting otherwise.