The Hagia Sophia is or was a museum since Ataturk. It is neither a mosque nor a church, so up to now it hasn't been possible for anyone to worship there. If it is converted back to a mosque I cant see how christians could worship there. It would have to be consecrated as a church to do that. My concern is the fragile state of this building and the damage that 100's of worshippers could do just milling around. There are also a number of christian images painted on the walls that could be damaged.
