The proposal involves replacing rule 3 with a new rule that requires the replacement package fee rate to be higher than the original transaction's fee rate and an absolute fee bump that covers the min-fee rate times the size of the mempool churn's data size. Rusty Russell raised concerns about blocking RBF with a large-but-lowball transaction, but others pointed out that OP_CSV with a relative locktime of 0 could enforce RBF on spending transactions. It was also noted that if the parent is RBF, the child inherits it. The consequences of dropping the heuristic were questioned.