Here we go again. Come the Ides of November, some subset of Bitcoin nodes will switch to an incompatible protocol that doubles the block size while retaining the compacted data structure of segregated witness, also known as segwit. (Back in August, a BitcoinCash fork was created for bigger blocks without segwit).
The upside of a decentralized currency is that no one can ever agree on anything, making it difficult to engage in shenanigans like open market operations and debt monetization. The downside of a decentralized currency is that no one can ever agree on anything.
If everyone collectively decides to change the rules, it’s consensus. If a subset of the population decides to change the rules, that’s collusion. Every user has a different threat model, and hence a different threshold for what constitutes consensus.