It’s in a very early stage, and you have to ask nicely to get the needed files, but it is beginning.
Check out these forum threads:
https://www.flashdevelop.org/community/viewtopic.php?t=725 (particularly the last page or two)
https://www.flashdevelop.org/community/viewtopic.php?t=796
The upgrade consists of a new ASCompletion.dll (provided by Philippe of FD) that supports some of the newer AS3 structures, and a set of “intrinsic” classes developed by Ben Clinkinbeard. Still needs some work, but it’s an awesome step in the right direction. Nice job guys!