Afaics, ignoring decentralized checkpoints should be plausible since the attacker would control the decentralized consensus.
Ignoring centralized checkpoints is not so feasible, since you've got to convince others not to run the reference client.
Applying the decentralised checkpoints isn't based on consensus though. It is a decision each miner may make on their own.
They can also be delivered out of band, so DDoS pfft.
It allows each miner to select which chain they like.
So if BCX forks with TW or other method, that fork ends up back where it started, back in the sandbox along with the little shovels, buckets, and Stoli empties.
There are certain further improvements to this innovation that may yet come, but the rapid response to the only plausible indicated threat (which isn't even all that plausible IMHO) remains an underrated achievement. BCX shares some of the thanks/blame for this forced evolution.
You said to me upthread you like disagreement. So please pardon that I need to point out that afaics miner's choice doesn't resolve the issue that once a 51% fork has run for a while and many users get their transactions intertwined with it, you can't untangle it to revoke it any more, especially given the anonymity with the ring signatures.
Sorry.