There's something weird here:

  root@nas-04:~ # ifconfig thunderbolt0 10.1.1.2

  root@nas-04:~ # ifconfig thunderbolt0
  thunderbolt0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
          inet 192.168.10.2  netmask 255.0.0.0  broadcast 10.255.255.255

The IP on the interface is different than the one that it was theoretically configured with. My suspicion is that perhaps the IP used was changed at some point and this is just an editing slip.

> Now that the interface has an IP, we have to add a static host route entry for it to communicate:

If both sides are configured with an appropriate netmask on the same subnet, there's no need for a specific host route.