I think I am done with Flex / Flash Builder. I havent heard a thing from Adobe about any plans for the platform tooling and there is a continual lag in the AIR and Flex for mobile support. I mean, just recently upgrading to xcode 5.1 broke the ability to use the iPhone Simulator which took a while to get fixed. You can make the argument its a beta cycle but should that test be part of Adobe's basic tests for functionality?
I have started my trial of Xamarin and have been working on POCs of some of the mobile components that I would need to continue working like I did in Flex.
If you add things like MvvmCross to the Xamarin equation you get data binding much like you do with AS3 / MXML.
The other added bonus is that xamarin can use its own tooling or visual studio and since they are a microsoft partner they are included in beta cycles so there is less of a lag with platform features / tooling, etc.
Sure, you have to learn a bit more about developing separate UI layers for each platform but you also get the bonus of better code reuse and windows phone / windows store and mac desktop, which are things you cant do with Flex and at this rate are things that may never come.
I may still use Flex for web stuff if it calls for it but I'm betting I can do most of it in html 5.
I find it very sad that I am giving up a platform that I have been involved with for almost two decades starting with future splash animator, but I can no longer begin mobile projects that have such a huge X factor for support and compatibility down the road. At least with the xamarin price tag comes peace of mind, you get what you pay for.
Goodbye Adobe AIR / Flex / Flash
You should really check out flash develop its free an open source (although doesn't work on mac ), it has excellent built in tools for mobile, you can also make cross platform gpu accelerated work very easy with starling.