I don't buy this argument, mostly because I've heard it used against both trans women, and even CDs. It just amazes me to listen to some loud-mouthed cisgender woman with a chip on her shoulder who chides one of us for trying to define femininity for her, who then turns around and defines it for me. (Hint: even if you are a cisgender woman, you don't get to define what it means to be a woman for anyone but yourself, really.)
I know several drag queens who are in transition. There isn't any way to tell who will or won't transition early on. I also know several drag kings, some of whom are also in transition.