@Rafal_
There are currently no plans for the C9. The OneMesh is being worked on so far for the AX11000, AX6000, AX50, and AX20.
You can connect two repeaters to the router either via Wi-Fi or Ethernet. Having all devices named the same will provide only one network to connect to for covenants. What separates a mesh network from a network with three nodes named the same is supporting the roaming protocols. If you look up the protocols 802.11k, 802.11v, 802.11r each gives a feature that allows for seamless roaming through your network. If you do not have a mesh network what will happen is you will notice network drops as your device connects to a different network node or the client not moving to a better AP.