Fact:
The cartel can hide how much hashrate it has, by using many IP addresses and sharing transactions until it has 50+% or more and is ready to move to the next stage.
Fact: moving to the next stage, i.e. announcing to the world that they do have 51% power, will be tantamount to them shooting themselves in the foot. Bitcoin will crash, as will their investments, OR they will be seen as hostile, and punished. IP or not, you can tell who has how much hashing power by how much each bitcoin address gets paid. The reason you can tell that BTCGuild, Ghash.io, Eligius, etc have so much hashing power is not from their IP addresses, but from the bitcoin addresses from the blocks they publish.
Let's say BTCGuild and GHash both owned 33% of the hashing power, and were actually owned by the same person, so you couldn't tell that someone owned 51% of the hashing power. What could this person do with these two pools that would not immediately expose them as having majority hashing/decision control, send bitcoin into a panick, and have miners leave those two pools en-masse?
So, if you are using an Amazon wallet app, and I am using some other wallet app, and you try to send me coins, how will I know whether you sent them if you only send them to Amazon's servers? It would essentially cut everyone using Amazon clients off from the rest of the bitcoin network. Why would anyone want to use such an app? Bitcoin transactions primarily work because they are propagated P2P through the network from person to person. Miners just sit on the perifere catching these transactions as they pass by and adding them to blocks.
Fact:
You are conflating the publication of block solutions with the propagation of transactions before the fact.
You are assuming that bitcoin wallets must wait for a solved block (~10 minutes) to see whether someone sent them money. That's not how it works. If your case was ever encountered, where you tried to use your Amazon wallet app to send me coins, and your app only send the transaction to Amazon's miners, I would claim that you have not sent me any money, since it hasn't shown up on the network (not within the first 10 minutes), and walk away, OR notice that your software is hiding transactions, and consider you suspect. Besides, with version 0.9 that's coming out, you would be sending me money from your Amazon app in the form of a signed transaction, and I would be the one to broadcast it. As a recepient of the coins, I have incentive to broadcast it to everyone I can, not just to your Amazon. So...
Fact:
If the cartel waits until they have 80 or 90% of the hashrate and transactions before attacking, then you will not get most of the commerce on your new fork. You lose.
The cartel's customers are not going to change which websites they send their transactions on. They will be happy with the service they are getting.
Fact: the cartel's customers will be VERY unhappy when their currency crashes 90% in value, as large holders and investors dump the now broken currency for something else. That is what you, and those guys who wrote the Selfish Mining paper, are ignoring, or refusing to connsider.
Cartels will own 100% of mining. No improvement at all for humanity. Worse we will be on a public ledger with no privacy nor anonymity. This is the 666 system.
How would miners know which address belongs to whom, if no IP's are tied to it, and their miners may only hear about a transaction after it has passed through multiple clients? And don't forget, if a 51%+ cartel implements nonstandard changes, their blocks will not be accepted by any of the clients, and won't even propagate. Their 51% will instantly become 0%, because, again, bitcoin rules are enforced first by the clients, and second by the miners.
None of that makes any sense.
This:
"Worse we will be on a public ledger with no privacy nor anonymity."does not work, because of this:
"How would cartel miners know which address belongs to whom, if no IP's are tied to it"There is no identifiable information that miners, even 100% miners, can get on people's bitcoin addresses. IP's are not tied to them, and neither is anything else.
As for this:
"And don't forget, if a 51%+ cartel implements nonstandard changes, their blocks will not be accepted by any of the clients, and won't even propagate. Their 51% will instantly become 0%, because, again, bitcoin rules are enforced first by the clients, and second by the miners."
if that does not make any sense to you, then you need to figure out how bitcoin and its distributed consensus system works, before telling others they don't understand how bitcoin works. I would explain it to you, but I don't want to waste my time on someone as full of shit as you. And that doesn't happen often.