I'd like to file a low-priority feature request:
It's possible for AS3 to "include" files in the middle of the source code. (more here).
I'd like to use some auto-generated code in my project, which, I figured, would be best placed in included files.
It would be great if FD provided autocompletion for the external included code.

Can I ask why you want to use include directive?

And how you want to solve file readability problems?

File readability remains a problem for manual use.

In my case, I have JSFL scripts that parse library and generate AS3 wrapping code for symbols. I can then "include" the generated code in my classes where I need it. However, this specific problem can be solved by using more OO aproach using classes.
By telling that it's "low-priority" I meant that it actually doesn't need to be done - I just wanted to leave this topic as a reminder what could possibly be done.