In theory you can do this, but my experience in practice is this isn't reliable. I removed a Nest WiFi Point and replaced it with a second Nest WiFi Router, setting up as a Point, with the LAN port going into a small switch to connect a couple of devices (an Apple TV and a Mac Mini). The next day, the entire network went down and even power cycling the routers/points would not bring the network back up. So, I factory reset the network and re-added the main router, an additional point, and the second router-as-point. Again, worked for a day and then total mesh meltdown.
I've verified that both routers are running the latest F/W. After two iterations of factory reset and then re-building the mesh, the network keeps crashing as I'm describing above. I replaced the second router with a Point and all is well (but without the LAN connectivity).
I have no idea what is going wrong, but am convinced that using a second router as a point has limitations for which I am not aware - I wonder if the second Router/Point wants to start acting like a Router, which brings down the mesh.
From what I've read on the way Nest routers behave this way (with their Ethernet ports) it doesn't sound like what you're describing is a great idea: https://www.googlenestcommunity.com/t5/Nest-Wifi/Nest-WiFi-Router-Ethernet-ports/m-p/111928#M10982
It's not the second router, I believe it has to do with how the networking occurs between the built-in ports.
Sure, but my second router has nothing connected to the WAN port - only the LAN port.
For what it's worth, I tried this again (factory reset, adding back in one at a time, et al.). Worked for 2 hours and then: crash. I unplugged everything, plugged the main router back in and get the slow throbbing light (i.e. waiting to start the setup process).
Enough punishment for me... moving on to another vendor/solution.
I'm checking in to see if you still needed some input in here or if the replies from the community go this sorted out for you. If you still have questions, just let us know. I appreciate all who have chimed in here!
I wanted to follow up and see if you are still in need of any help? Please let me know if you are still having any trouble from here, as I would be happy to take a closer look and assist you further.