Its actually the P2P network that is filtered out, by MARA slipstream (and direct submission and private mempools).

Today, MARA will "pre-announce" the next block, for free. This is useful.

But they could (theoretically) charge $ for that service.

And then Luke would be saying that Mara should pay him [ and each of his nodes] -- but he would be wrong.

It is the full nodes which need the mempool of the mining nodes (to save on bandwidth)