>
>
> With full-rbf, who saw what transaction first doesn't matter: the higher
> fee paying transaction will always(*) replace the lower fee one. With
> opt-in RBF, spamming the network can beat out the alternative.
>

incentivised predictability is critical when designing low level protocols,
like bitcoin.   the knock-on effects of deeper, network-wide predictability
are likely beneficial in ways that are hard to predict.   for example stuff
like the "sabu" protocol might even work if full-rbf is the norm.