I haven't read your reddit posts so I can't comment on those.
Well, I see now why you keep claiming that millions of users would revolt.
You're rhetoric is utterly ridiculous.
Upgrading a piece of software is not "revolt." People upgrading in response to an instance of obvious abuse are not "rebels," they are ordinary users.
In that scenario that I described, the "protective improvement" to the protocol would be proposed by the cartel sometime before the next halving. By that time, the network will still be supported by money from the new adopters who buy the coins produced by the miners. Which coins would those new users rather buy: cartelBTCs, that live on the largest network built by man, using (almost) the same protocol designed by Satoshi, wich has been tested for more than 6 years; or rebelBTCs, that live on a small CPU/GPU network, using a radically different protocol that was patched together in three days and has been in used for less than a month?
You are completely confused. New users would be the ones with the easiest upgrade path -- just install the current version. Furthermore they would want the version of software that interoperates with all the other users.
Users don't care about mining, and every wave of bitcoin users cares even less. Your whole mining-centric view of bitcoin is as bad as the people who see mining and immediately respond "free money from the interwebs!"
In fact your "cartel" has much more to lose from attempting to do this. Not only the potential loss of their equipment value, but simply the guaranteed value at risk of burning electricity to accomplish that
might not work.
Finally, a CPU/GPU network supporting bitcoin would be neither small nor insecure. It wasn't then (during the GPU and CPU eras) and it wouldn't be now. It is easy to make silly comments about "the cartel would just rent cloud mining and attack the network" if you have never seen what happens in the cloud mining market when even a small altcoin shows a bit of success. Let me give you a hint to get you started: most of available cloud mining capacity (and it isn't really that much) would already be mining bitcoin honestly (for mining profits).