Bit of necro, but this thread also comes up basically #1 in google searching for AIR+flutter.
I also started using Flutter for my private client projects as alternatives like React Native are even more of a hassle (and basically no first party support for issues).
It has its issues like any other framework, you can see that the team behind it was VERY inexperienced 4 years ago when they started (some google engineers even said so themselves on reddit).
Time will always tell, but google has some bigger projects already using Flutter internally (e.g. Google Pay, Stadia) and is currently developing a new OS that is supposed to replace ChromeOS and Android (Fuchsia) - completely based on Flutter!
Flutter can also be used for Desktop Apps, Web and even compiled for embedded systems like Raspberry.
There are other big advantages. E.g. you do not need to rely on plugins at all. Platform channels are quite powerful (native calls from Dart directly; but less performant of course), and of course you can simply integrate native ios/android libs into the project.
Reactive programming for gaming feels 100% off, as on every change in the ui, you have to rebuild the whole ui.
This is kind of wrong though and feels like you just skimmed over some doc.
You do not ever have to rebuild the whole ui, that is literally why there are widgets. The data binding is well enough done, e.g. if you move a figure and its coordinates change then only this one figure widgets will rebuild. Flutter also is smart enough to detect if widgets have to be rebuilt at all or simply use the cached version. It is way smarter and performant than Starling that way.
You also do not have to use this. You can control data binding and re rendering at any point, or simply do not use it at all. No one forces you to use stateful widgets. No one forces you to use any provided widgets from Flutter. You could create constant stateless widgets, manage all state manually in e.g. model classes and trigger any render yourself... like you do in AIR, just even more controllable.
For games you'd use Flame anyhow, which you can plug into any widget at any point and has its own render and update cycles you can control like in any other game engine.
I'm currently finishing up a client project with over 450 classes and around 70 different screens. Not a game in there (I'm planning some with Flutter though), but I reach render speed of complex screens of 1.4ms/frame on an old iphone7 and around 4.3ms/frame on an iphone 5s! I want to see AIR repeat that. to be honest. Performance should not be an issue.
