My theory on iMessage with the new 894M BIOS is that it probably works fine on a clean install. But for those those of us who had already gotten iMessages working through the fix posted on the Wiki, the new BIOS breaks iMessages. I have not tested this theory because I never use iMessages and don't feel like doing another clean install, as I had just done one days before the new BIOS was released. I could very well be wrong though. It's just a theory.
That was my experience getting it to work again.