I’ve been communicating both on Crossbridge forums and with my Adobe contact, who was nice enough to speak with the Adobe internal team about the issue crippling multithreading in FW. I sent him link to FW online demo so the team has something to test this issue against. While they said to check the issue no clear date or timeline was given yet. This bug was a deliberate change to tighten security, but as a side effect it broke all C++ -> Flash crosscompiled apps using multithreading, like FlashyWrappers for Flash Player.
Everyone who can spare 5 minutes please sign up at Adobe(as Flash / AIR developer you probably are signed up already) and vote for this bug:
https://bugbase.adobe.com/index.cfm?event=bug&id=3938269
Thanks!