I think the point there is that if Chrome doesn't trust that CA, then the servers will need to be updated to use a different CA, which will break clients that pinned the old CA.
Or maybe I've misunderstood the situation.
I've always been of the opinion that the rogue/careless CA problem can be solved by mandating N root sigs and recommending M>N. In a system with multiple independent LetsEncrypt like entities this is doable. If a CA needs to be revoked you can do it in a much easier way here, since it's still ok to transitively allow sites with N-1 certs and one now-disallowed cert signed by that CA. Doesn't fix all the problems but it certainly removes the inertia behind kicking out bad CAs.
Looks like we'd need a x509 extension to do this then. :/