Earlier quoted context omitted.
Open sourcing it won't help preserve content - that's far more effectively achieved via VMs and using the archived players which Adobe provide (and will hopefully continue to provide or allow preservation of on abandoware or other sites). Maintaining the build systems, compatibility layers and so forth won't be easy (Adobe often couldn't manage it), and bug fixing in the code is a risky prospect for preservation as i…
Not sure if you know but Adobe open source the Flex framework, is now part of Apache and it continued to be used in projects. If Flash and AIR could be open sourced, we could ahve an alternative for GUI application development(nothing wrong with choice) and AIR could compete with Electron
AIR did hold promise, but ultimately suffered from being terribly cumbersome to extend when you wanted to access native features or platform standard libraries (I've created several AIR native extensions over the years).
However, one of the big problems with using Flex or AIR after Adobe have end-of-lifed Flash is that you're going to lose access to the content creation tools. There are some alternatives (FlashDevelop and FDT for coding, I forget the name of the attempt at an open source Flash timeline editor), but nothing is close to being as good as Adobes own tools when you want to.
If you want to leverage knowledge of ActionScript, people may be better off looking at something like Haxe for cross platform gui app dev.