I think his ult should give a temporary Crowd Control reflection to his target, get rid of the Revenant, same revive without the ability to use the revenant to body block skill shots and we lose the damage from the revenant for more reliable way to engage. In turn it should summon a copy of each of his ghouls (so if he uses it after every other skill he could have 6 ghouls up for a short duration), and his current passive of damage reduction should be shifted into the ult so he gets the buff only during ult times. This make windows of killing him in laning, provides him with a unique ultimate that serves as a powerful tool for nearly any kind of team but best used against high CC teams (low CC teams will just burst the target down with damage, where this would be less useful.
I want the ultimate to truly feel like an ultimate and also make it look really epic, maybe a massive scale increase or deformation to the target elongating them vertically so they appear to tower over enemies and yet be narrow (like a skeletal harbinger of death kind of idea) though I don't know the extent of their deformation tools in game, they would likely just have to settle on a particle effect instead.
The entire idea revolves around a different kit designed to be more of an initiator juggernaut but just by running in waving his shovel around at a slightly frightening speed.
Some things to know about my crowd control reflection idea, forst it doesn't remove CC already on a target or himself, so using the skill before engaging or being engaged upon is better. Second, it only lasts a few seconds and changes the way teamfights are fought (CC the incoming hostile, to kite the hell out of it). Third, the extra ghouls all would apply additional stacks of their effects so it makes for interesting play.
As a side note it might be an extremely interesting idea if the ghouls were more like Zyra's plants in that they were summoned but didn't move, instead performing their effect and attack in the direction they were summoned (or on my proposed ult, around the targetted friendly pointing outward in each direction from them). Also, to encourage a juggernaut build having the ghouls attack speed scale with his total health means the percentage damage proposition then gets stronger both just for levelong and also by building him healthy (currently assassin like builds on Yorick can be extremely frightening by literally 2 shotting carries while being unafraid to die due to his current ult). I really like the idea of an attrition Gravedigger that has a defined time of being really dangerous and removing the AI element of his damage from ghouls means being able to play around them in lane (rather than run to a bush or away from him)
I could go on and on with ideas for him and tuning him in a variety of different ways, but the main recurring ideas involving removing AI controlled damage, increasing counterplay and outplay options both for and against Yorick, and focusing on giving him a solid means to engage.
is really lacking is any kind of stick everyother champion either has some form of gapcloser or just straight up better cc (i count 
mini jump ) so i suggest giving him a sort of build up combo passive that all culminates on his Q.
For instance based on the order of spells/ghouls hed use there would be diff effects im thinking omen of pestilence into omen of war would give out a short mini stun but with a sorta diminishing stun effect like kennens stun effect so that it wouldnt be abussive perma stun/slow. As it stands now you need to land your WQ or anyone can just walk away from some might dash for the hell of it almost like a free taunt, but with tenacity, de aggroing ghouls and 
being popular getting in range to land a Q is harder and with out that you have no engage or damage. on the flip side ive no idea how a new ult would work i was thinking ghouls would swarm around him to help with the passive or hed like dig a grave coming up blank on that one but i know im probably years early on any real yorick rework talk but these where my thoughts
[zombie-brand-clap]
