I mean Ryze got an update April 25th, 2015 and Yorick still hasn't been updated, not to mention no skin for over 1617 days (as of 7 monthsish ago) for Yorick. The fact that Yorick is being put off in front of yet another Ryze update makes me 
#MakeYorickGreatAgain
Yorick got started first, but Ryze didn't need all that much work comparatively. There's two teams for updating champs, and Yorick is one hell of a mountain to climb since you need to update not only his model, but the models of all his ghouls.
Like people have stated, Yorick has been looked at for longer than Ryze but it's harder to update him in a way that makes him fun to play and play against while keeping the core of his character as an undead summoner.
Yorick was not put back by Ryze. Ryze was going to go right now and Yorick needed more time. Yorick wouldn't have come any sooner no matter what.
Yorick also did not get a skin because once he gets a VGU they will have to remake the skin. Plus they don't want to promote Yorick being played along with the fact that not many play him.
Yorick's rework was not held back by Ryze, it needed more time. His rework would still come out the same time it will even if Ryze wasn't going to get a rework.
Yorick is a much more difficult champion to update than almost any other.
