Actually, something I've been mulling over recently, is it possible in the Abrams movies, the writers just don't know what a navigator is and why there has to be a separate person from the helmsman to cover this role? In Trek XI, even though Chekov is the navigator, none of his input in the movie in the movie really reflects this role, aside from possibly the warp bounce or whatever off Titan. And then in STID Chekov gets transferred to engineering and the replacement navigator is not a speaking part in the movie. So, if anything, assuming they do decide to just write Chekov out with a transfer to Reliant or whatever, I don't actually expect a replacement for him.