Hello. Well apparently, The Apocalypse will give heavy focus on Mystique and Magneto's blossoming romance. Her and Beast's bond will have a setback.Yes, introducing us to Nightcrawler and then later finding out that he is actually the son of Mystique is not going to be on the level of the Star Wars reveals, but for the general audience, who has no real knowledge of the comic canon, it will be a slight shock.
More importantly, in this movieverse, the conception of Kurt was likely caused by the events that were caused by Erik choosing to leave Mystique and the Brotherhood. Yes, we know it was because he was trying to save Kennedy, a fellow mutant, but Raven never knew that. From her point of view Erik choose to leave her which would likely lead to some negative feelings.
So my point is that Kurt's parentage most likely applies to the story and to the resolution between Raven and Erik, which makes me think 100% that it will be included!
They want to bank on the star powerhouse status of JL and MF, for the franchise.