Morrison's work is generally really great so I don't see it being a problem as long as he doesn't take the title FROM Gail but has his own.
The big problem I think is that Grant doesn't tend to write Wonderwoman himself it's always when she's on teams or in large casted books and his story telling works into making things large and almost impossible to believe stories like Seven Soldiers or Whatever Happened to the Caped Crusader. He knows how to do so with Superman and Batman since they're very very archeypical the godlike alien or the ultimate human etc...but he doesn't quite understand how to do so with Wonderwoman.
I think this'll help him understand the character.