The new "emergency RBF" rule:
6. If the original transaction was not in the first 4,000,000 weight
units of the fee-ordered mempool and the replacement transaction is,
rules 3, 4 and 5 do not apply.
This means:
3. This proposal does not open any significant new ability to RBF spam,
since it can (usually) only be used once. IIUC bitcoind won't
accept more that 100 descendents of an unconfirmed tx anyway.
Is it not possible for Alice to grief Bob's node by alternating RBFing two transactions, each one placing itself at the bottom of Bob's top 4,000,000 weight mempool which pushes the other one below the top 4,000,000 weight, and then repeating with the other transaction? It might be possible to amend this proposal to partially mitigate this.