I thought exactly the same, but the problem I foresee here is what I linked to in my initial post. This post reveals that Google WIFI needs to remain as the device provisioning DHCP leases or else the mesh network starts to fall apart! 
I did read somewhere, and I'll have to search for the link, but someone was apparently able to install the Brume 2 as just another device attached to the Google WIFI router -- as an aside, am I correct that this would means the Brume 2 is "behind" the Google router? -- but then used some crafty portforwarding or drop-in gateway magic(?) to (1) allow the Google Router to to continue to control DHCP assignments but somehow still route traffic from all devices attached to the router through the Brume 2 to take advantage of it. I didn't quite understand it, but does that sound like something that is even possible? It seemed counterintuitive to my visceral thinking that traffic is routed forward and not somehow backward, which is why I assume that I'd have to place the Brume 2 or Beryl before the Google Router so it passes through that device and gets encrypted before it hits the router.
Does that make sense?