From BIP 125:
A transaction is taken into account to have opted in to permitting substitute of itself if any of its inputs have an nSequence quantity lower than (0xffffffff – 1).
The nSequence in a transaction is used for different issues together with locktimes so it’s unlikely to ever be eliminated completely.
In case consensus determined to disregard pro-zeroconf nodes (in case that’s or could be a factor),
then what is the level of getting the RBF bit in a transaction, if every thing within the system is implementing RBF (both explicitly or implicitly)?
“Ignoring professional zeroconf nodes” does not make a lot sense until they’re making an attempt to vary the consensus guidelines or in search of to reject blocks with replace-by-fee transactions in them. In that case we’d be in consensus rule “battle” territory like with the block dimension wars however that will be a really unusual path to take given altcoins like BCH exist already which are not in search of to scale off-chain and are maybe extra open to prioritizing the zero conf use case. It’s potential full nodes may preferentially peer with different nodes who’ve the -mempoolfullrbf choice turned on in future. Nonetheless, within the Bitcoin Core 24.0 launch it’s off by default and there’s no preferential peering based mostly on this situation.
Would the RBF bit be then set for removing in a subsequent mushy fork?
It would not want a mushy fork or a consensus change to easily ignore the transaction signaling for RBF by default in a Bitcoin implementation like Bitcoin Core. I very a lot doubt Bitcoin Core would ever make RBF a consensus situation, it’s a mempool coverage situation. It’s potential Bitcoin Core may change coverage defaults and coverage choices out there to customers in future. That is pure hypothesis after all although, I do not know what is going to occur sooner or later and nobody can communicate for Bitcoin Core, definitely not me.
And if that have been the case, why not take away it the primary second pro-zeroconf nodes are ignored?
It’s potential the default for the -mempoolfullrbf choice might be modified in future and additionally it is potential the -mempoolfullrbf choice might be eliminated in future. As I stated, we’re shifting into speculating future adjustments in Bitcoin Core releases. Any future change would wish to have a pull request opened, reviewed, merged and included in a launch. As you acknowledged that is within the realm of coverage and never consensus so I extremely doubt this may be related to a future mushy fork however I suppose there’s a speculative ingredient to that too as I can not envisage each potential future mushy fork design.
