I can't believe that this isn't implement yet. I found post dated from 2014 asking for that feature.
Im stock as well. Want to use designer to export ''faceplate'' design wihch require ''.DXF'' file. But unfortunately just because of that I have to export to .PDF then import back into illustrator with sometimes unexpected results.
Hey dev team, what are you waiting for ?! Hey don't forget to have the option to convert ''spline'' into ''polyline''.
Come on there is so many people which are waiting for that single feature to make the switch from AI to AD.