> I would have assumed that this function mainly migrated onto one of the popular blockchains with clients using one of thousands of available gateways for reading.

Why would you want to use blockchains for this? DHT has been used for distributed c&c for ages and is generally a much lighter option.

But no, P2P C&C is still not really typical. In practice, there's mostly not that much need for it. Also, FWIW, for practically all use-cases P2P C&C discovery is a vastly better option.