This has been mentioned before (https://github.com/openfl/openfl/issues/146), but may be good to revisit.
Would it be wrong to build an implementation only for Flash and HTML5, or should it pass through Lime?
P.S. Here is an example of a file picker in AS3 using FileReference : http://www.kirupa.com/developer/as3/loading_files_disk_pg1.htm
We should have FileReference support now for Flash, Windows and Mac. We could have Linux if we sorted out how we’ll reference GTK, and I believe we have some support for saving files on HTML5, but there are some limitations there. Would be happy if anyone is interested in finding ways to improve what we have. OpenFL relies upon Lime’s FileDialog API in this regard – so that’s where work goes 