Lee Brimelow tweeted "we're working on Air for Metro. It should be available first half of next year."
(Metro is now called Modern.)
This may or may not cover Win8 RT on ARM in Modern mode.
A sad announcement for AIR recently:
"Adobe AIR is available and supported for Windows 8 Desktop on x86-based computers. Adobe currently has no plans to support Adobe AIR for Windows 8 Modern UI applications."
What is implied but not said in that quote is that there is no AIR on ARM, either.
More about it on this thread: