Comsent by whom? In most "decentralized governance" projects I've heard about, all you need is for the holders of 51% of the tokens to agree, and the holders of the other 49% have no recourse but to leave.
No, that's completely different thing. Mining power only "decides" about the blocks in the blockchain. 51% is only relevant in the context of taking over the blockchain by 51% attack.
Software versions and updates require social / economic consensus and have nothing to do with mining power. Bitcoin is open-source protocol / software and everyone can use whichever version they like. But there's also economic incentives to use the most used version and to make sure that it will keep being the most used version, i.e. forks are bad and should be avoided, therefore it's in everyone's interest to reach consensus.
So there are two different places that a coup against bitcoin could occur? Processing and Software.
With something like 45% of processing controlled by entities in Iran, China, and Russia, it seems like an absolute fools game to put any significant wealth in Bitcoin. All it would take is a significantly effective worm to destroy bitcoin. But hypers gonna hype.
It's the same as any currency. If the place you want to spend it only accepts currency y then you must trade for currency y to spend money there.
Since Bitcoin is software anyone can fork it and create a currency y with the same ledger up to the fork but few people do because convincing other people to trade for it without a very strong argument is hard.
Yes, but I was talking about "decentralized leadership" in all the projects following Bitcoin, which often use 51% of stake instead of 51% of mining capacity, under the social theory that the biggest stakeholders will be the most invested in the outcome of the project.
Those with at least 51% of the sustained hash power can already redefine “Bitcoin” to be whatever they want… At any time whatsoever? (assuming they stay cohesive enough as a bloc)
That statement is a bit misleading. The damage an attacker can do through a 51% attack is much more limited than that. It allows an attacker to censor transactions or perform double spends, but it does not allow them to "redefine Bitcoin" (e.g. change consensus rules, arbitrarily reassign coins, etc.).
Anyone can do that, it doesn't require 51% of the hash power. And it's already been done hundreds, if not thousands, of times (the more technical term for them is "shitcoin").
