I can see the appeal of Adobe Air and its ecosystem. I guess on mobile the only problem is binding to system services & ad providers. IIRC most of that is already covered by 3rd parties, but it's a bit involved to do it yourself.
Funny you mention Flex, still gives me the shivers, still used by a lot of enterprises around here. Pretty much on par with applets in terms of badness.
Hey.. actually I also just got the task to integrate an Ad provider in out game and made a little research. As far as I can see almost all big companies are providing Adobe Air SDKs for integration. For Example:
Yes.. as far as I can tell most of this bindings are covered by native extension of 3rd parties. Not always free (but not that expensive), so u have to buy an extension for a quality FacebookSDK integration for example. Still far cheaper than for example Xamarin.
But considering that you do not necessarily have any costs in developing Air (you get the compiler, and also good editors, for free) it is not that bad at all.
I also do not write native extensions myself, but at least you know there is the option in case u need to access some native library. But yes, in that case it is not really "write it once" anymore.
Funny you mention Flex, still gives me the shivers, still used by a lot of enterprises around here. Pretty much on par with applets in terms of badness.