Obviously, and so we are back to what I already stated, which apparently you didn't bother to read.
1) There are two competing chains where one chain has only the attacker's blocks and the other chain has the honest miner's blocks. The goal of the attacker is to make their chain with their inclusion rules the longest. The network here can optionally choose the honest chain (which is what Gavin's proposal does). It also require 51% to pull off, which I don't think is possible anyway.
Which is the only possible path. This path both requires at least 51% of total hashing power, and it requires that the honest network (users, P2P nodes & miners) to ignore the 2nd chain with all transactions included. Neither of these are likely IMHO, and why the attack fails.
You
still have not read my reddit posts, did you?
Summarizing them: Say the cartel has hashpower 0.54 * Z where Z is the total. The cartel first warns users that starting from block N, there will be a change in the protocol. The only substantive change will be the block reward, that will continue to be 25 BTC, for another 2 years, instead of dropping to 12.5 as originally planed. This change is actually necessary and good for bitcoin because the network is in grave danger bla bla bla. The cartel warns that users and miners who upgrade to the new version of the software, anytime before block N, will see no change at all. Users who do not upgrade will see no change until block N, but after that their transactions will not go through, or will be confirmed an then unconfirmed -- until they upgrade too. Starting from block N, miners who have not upgraded will not earn any rewards, until they upgrade too.
......
This is quite simply an insane position to take. You've created an imaginary world that does not exist in the real world and used that to extrapolate and predict behaviors that are completely opposite to how people and the ecosystem have behaved in the past, which is the predictor on how they will behave in the future.
What you describe is not even a +51% attack, it is a demand for a forced hard fork from one miner telling millions of other people what software to upgrade to. That is simply the most absurd thing I've ever heard. And the reason you think this will happen is because if that one miner claims "this change is actually necessary and good for bitcoin because the network is in grave danger", that would be accepted by the general public?
What would happen in your example is the millions of bitcoin participants would tell that one miner to take a hike and continue with the existing P2P core protocol. Then when that miner started to produce nonconforming 25BTC blocks, they would simply be rejected out of the P2P network as invalid, and the honest network would carry on. The attacking miner could have 95% of hash power and it wouldn't matter, his blocks would be rejected as nonconforming and the network would simply re-adjust to the 5% remaining. You do not even understand the basics of how a potential 51% attack is limited in it's range of attack vectors in the real world and how those limited attack vectors are harmless/manageable.
You then claim miners and users who do not upgrade would have their transactions blocked. Again this is insane. What would happen is those miners and users would confirm transactions on their own honest chain (the original chain) and not care whether their transactions confirm on the attacker's invalid chain.