Perhaps I am closer to describing more specifically how a BCX-like an attack might be feasible. Note I still haven't done any precise quantification so interpret this as probing FUD.

A key algorithmic insight may be that the attacker's hidden fork is evaluated when it is published according to difficulty in place at that time, not the difficulty that existed while the attack was mining the hidden fork.

TW and other difficulty adjustment attacks are based on lowering the difficulty at which the attackers fork is measured, non-linearly relative to the proportion of the attacker's percentage of the network hashrate.

For example, the attacker could introduce a lot of orphans and cause the network to waste hashrate, thus lowering the difficulty at the next adjustment.

Or the attacker can leverage flaws in the difficulty adjustment that cause the majority to mine at a higher difficulty than the majority's hashrate, then the attacker publishes his hidden fork when the difficulty readjustments. For example, Kimoto Gravity Well has a flaw in that it thresholds the adjustment so the attacker can trigger a huge difficulty raise, then pull his hashrate away but not too fast so the difficulty adjustment stays under the threshold and doesn't adjust until the attacker is ready for it to.

I believe the discarding of the 20% tails of the timestamp distributions in Cryptonote's difficulty adjustment might present such a flaw, but I am not attempting to quantify it and prove it (not my job). Imagine that every distribution of timestamps follows some bell curve. So if the hacker puts his timestamps on one side of the mean, he can shift the mean.