They might not even address it at all and continue with their current weapons/props check-in policy.
For those bringing props and weapons, it might be a safe bet to dial it down a bit given recent incidents. I was thinking of being Nick Fury for a day (who has guns), so instead of the firearms, I'll just bring the Tesseract instead.
This is correct. They may make no changes, they may make sensible changes, or they could go crazy and make us act like we are at an airport. I would say hope for the best, plan for the worst. Aka, find a costume that is sensible for the times we are living in, aka if you can do a costume that doesn't need realistic guns you are probably on the right path. But if you want to be say Rick Grimes, maybe just leave the shotgun at home this year.