When you say that a special relay network might be more "smart about
replacement" in the context of ANYPREVOUT*, do you mean these nodes could
RBF parts of a package like this:


Given:
 - Package A = UpdateTx_A(n=1): txin: AnchorTx, txout: SettlementTx_A(n=1)
-> HtlcTxs(n=1)_A -> .chain of  transactions that pin UpdateTx_A(n=1) with
high total fee, etc.


And a new package with higher fee rate versions of ANYPREVOUT* transactions
in the package, but otherwise lower total fee:

 - Package B = UpdateTx_B(n=1): txin: AnchorTx, txout: SettlementTx_B(n=1)
-> HtlcTxs(n=1)_B -> low total fee package


Relay just the higher up-front fee-rate transactions from package B which
get spent by the high absolute fee child transactions from package A:

 - Package A' = UpdateTx_B(n=1): txin: AnchorTx, txout: SettlementTx_B(n=1)
-> HtlcTxs(n=1)_A -> ...chain of up to 25 txs that pin UpdateTx(n=1) with
high total fee, etc.

On Thu, Aug 6, 2020 at 5:59 PM Matt Corallo via bitcoin-dev <
bitcoin-dev@lists.linuxfoundation.org> wrote:

> In general, SIGHASH_NOINPUT makes these issues much, much simpler to
> address, but only if we assume that nodes can
> somehow be "smart" about replacement when they see a SIGHASH_NOINPUT spend
> which can spend an output that something else
> in the mempool already spends (potentially a different input than the
> relaying node thinks the transaction should
> spend). While ideally we'd be able to shove that (significant) complexity
> into the Bitcoin P2P network, that may not be
> feasible, but we could imagine a relay network of lightning nodes doing
> that calculation and then passing the
> transactions to their local full nodes.