The consensus is reached when the majority of a group agrees to something or to do something.
I agree it is confusing, but in my post above the word "consensus" is referring to the consensus rules as hosseinimr93 has explained, and not to a "general agreement" between all node runners. RBF rules are a local policy, and even if 100% of nodes enforce the same RBF policy, a block containing a valid transaction which breaks that policy (such as a replacement transaction which evicts >100 other transactions) will still be valid and will still be accepted by all these nodes because it does not break the consensus rules.
You might be interested in reading this page:
https://en.bitcoin.it/wiki/ConsensusAn upper limit means each node would have to keep track of all previous replacements, and not every note may have seen all of them. So it won't work.
This was actually the original use of the nSequence field in transactions. Any unconfirmed transaction which had an input with an nSequence of less than 0xFFFFFFFF was not yet considered finalized and could be replaced by a conflicting transaction with a higher nSequence value. And so the upper limit was effectively 4,294,967,295 (0xFFFFFFFF in decimal).