Good comment on testnet. From what I understand, I don't think that's all the plan for the these clusters. Otherwise, why do they specify this?

> When two clusters share a common genesis block, they attempt to converge.

More importantly, the cluster is only 150 validators:

> A Solana cluster is capable of subsecond confirmation for up to 150 nodes with plans to scale up to hundreds of thousands of nodes.

This is not comparable to Mempool where it is in your best interest to broadcast a transaction across the network. Yes, everyone sees the mempool but it doesn't allow you to manipulate transaction order as long as the original sender has paid a high enough fee.