I'm going to be straight up simple.
Will he keep his ghouls mechanic, or will he have a completely new mechanic, completely new abilities?
FYI: Sion got to keep his permanent HP when killing a minion and his shield detonate. Will Yorick keep something from his past?
Why did you make me remember this song? WHY!? https://www.youtube.com/watch?v=LDiDK_yBCw0
I hope it's in your head forever.
I'm sorry, "soon™"?
Riot's recent replies on the subject have been far closer to "after we rework almost everyone else we can think of" than "soon".
They put out the player thread asking what Yorick players liked the most in playing him etc. etc. I know the ghouls were at the top of the list for player fantasy! Last I heard Yorick's new kit ideas were going to work somewhat like Elise and her Spiderlings? He gains some every few seconds and they empower or change the way some of his abilities. Then his R opens a grave and summons and army of them. That was awhile back though... and these things almost never come out the same as their ideas, so I could be vastly different by the time we actually get new Yorick.
I think it was Xelnath doing Yorick work if you wanted to look for his posts, he was posting kit ideas and looking for a lot of community feed back :)
All answers (or as close as we can get) are here... should you be brave enough to dig through 400+ pages of comments http://forums.na.leagueoflegends.com/board/showthread.php?t=3605329&page=1
