Based on the information I could gather about about the MW12 from user reviews, etc., the MW12 appears support both wired and wireless backhaul with other MW12 nodes. The MW12 has three Ethernet ports, so with the above diagram, it should be possible to connect both the TV and computer to the secondary node, in addition to the wired link.
For those that currently have MW6 or lower model nodes, I have come across many reports of stability issues when adding MW12 nodes to the mesh, regardless of which node acts as the primary node. So for those who currently have MW3/5/6 nodes, I suggest only adding further MW6 nodes or be prepared to replace all the nodes if upgrading to the MW12.
Finally, from my own experience, the Canon G4510 and G4511 printers both have wireless stability issues with the Tenda MW6, even just one room away from a Tenda Node. It is the only wireless device we have that doesn't get along with the Tenda Wi-Fi. As these newer Canon printers don't have an Ethernet port, I set up an old TP-Link 2.4GHz wireless point just for the printer as a workaround. So far we haven't had any further issue with it.
For those that currently have MW6 or lower model nodes, I have come across many reports of stability issues when adding MW12 nodes to the mesh, regardless of which node acts as the primary node. So for those who currently have MW3/5/6 nodes, I suggest only adding further MW6 nodes or be prepared to replace all the nodes if upgrading to the MW12.
Finally, from my own experience, the Canon G4510 and G4511 printers both have wireless stability issues with the Tenda MW6, even just one room away from a Tenda Node. It is the only wireless device we have that doesn't get along with the Tenda Wi-Fi. As these newer Canon printers don't have an Ethernet port, I set up an old TP-Link 2.4GHz wireless point just for the printer as a workaround. So far we haven't had any further issue with it.