AP filled with CB Halloween hatchlings?? Maybe there will be a few CB eggs but definitely not filled with hatchlings, if you meant bred halloween eggs and definitely. Judging from the previous years, there are always people missing the Halloween drop and the people who are there to catch the CBs generally don't AP the eggs unless they're code hunting. The few CB Halloween eggs that appear in the AP are grabbed almost instantly.
CB Halloween up for trades after their initial drop is over is generally very pricy, at least from what I've seen. I definitely wouldn't compare Xenowyrms to CB Halloweens, Xenowyrms are a permanent release and available whenever, no matter how uncommon/rare they are at the moment or in the future. CB Halloweens are available only once and there are no restrictions for them unlike the other holidays, they have a lot of tradability.
I've been trading for CB Halloween hatchy IOUs for awhile now (I have a total of 51 now) and I can say at least from my own experience it's going to be hard finding someone willing to trade IOUs in exchange for Xenowyrms/Coppers, though probably not impossible. The things I've seen success in trading for IOUs with are CB Silvers, 3rd gen Prizes, Neglecteds, etc. And for a little amount, maybe 2nd gen Metals from pairings people need specifically.