Well logically, if Dawn is The Key, she should be able to open any Gate. She's a walking Tesseract. But this a good thing if she can control it, because then nobody could trap her or use her against her will. She could just step away, or open a Gate under their feet.

Plus it would cross over really well to any other setting with Gates or dimensions: Marvelverse, Schrodinger's Heroes, Stargate, etc.

... you should totally write more of this. :D