The EOS GitHub contains descriptions/diagrams of three network topologies, namely a "star" topology, a "ring" topology, and a fully connected mesh. Are there any plans for any other systems, such as Ethereum's Kademlia-like networking, so as to support networks with larger numbers of validators or peers?
The EOS software doesn't define or require any the network architecture, that is completely decided by launch implementations. The current proposal for the mainnet EOS chain (being engineered and launched as I write this) will be based on a p2p topology with a mesh component. It's possible in the future there can be other network architectures for this chain, and certainly there will be other chains launched off EOS software.