I've been out of the Marvel Comics loop for years, however, the following women could be used since they once donned their own Spider-Woman costumes in the previous Spider-Man comics. All Marvel has to do is just revive the characters (if they haven't done so by now.)
Jessica Drew - 1st Spider-Woman
Jessica Carpenter Cornwall - 2nd Spider-Woman / Arachne
Martha "Mattie" Franklin - 3rd Spider-Woman
Plus a Spider-Girl.
Anya Corazon - 2nd Spider-Girl (Since Mayday will probably be left out, even though she was the 1st Spider-Girl.)
With all of that typed up, I don't see why Mary Jane has to be the next Iron Spider candidate.
http://marvel.wikia.com/
I guess I can rely on both Osborn's donning their Goblin threads, lest Stormin' Norman also takes up the Iron Patriot armor.