The article makes a reference to the failed ARC (Authenticated Received Chain) proposal which was intended to help DKIM not break email forwarding:

https://www.ietf.org/archive/id/draft-adams-arc-experiment-c...

It will be interesting to see if Google can be convinced to move away from ARC to something else. Gmail is all about email server reputation these days so they can reliably treat email servers they don't like badly.