Even if the new jungle items in season 5 favor tank champions more, Zac still won't be played because he doesn't bring anything good to the team that another champion doesn't.
The only unique thing about him is his E, because it allows him to gank from unexpected places. But if the opponent can see Zac channeling this ability, the charge up time and travel time create a situation where Zac should never be able to land the ability. In addition, the channeling nature of the ability makes it useless when trying to run away. It also can't really be used to chase for the same reason; the amount of time it takes to charge the ability negates the distance Zac crosses.
Previously, the good thing about his ultimate was the damage and the fact that any CC you aimed at him was ignored. Now it does no damage, and since he can be CC'd normally during the ability, this move doesn't really do anything special. His ultimate is out done by naut's ulti, sion's ulti (and sorta Q), sej ulti, ammu ulti.....the list goes on. This ability in its current state does nothing. Oh, wait, the only thing it does is create a lot of blobs to pick up, but thats about it.
I actually don't mind the fact that he uses his health, it actually baits a lot of people into trying to finish off Zac and the healing he does get, especially with SV, is pretty good.
They need to get rid of his AP scalings and have him scale off health. I think it would be very interesting to have % current health scalings. Similar to his appearance, he would deal more damage the higher health he had. it sorta fits, a giant blob is hitting you, its gonna hurt more if he is giant than if he isn't. In the worst case, he would be doing the same amount of damage he does now (because no one builds AP on him) and he would be able to deal tons of damage at high health, but since his abilities cost his health, he would lower his damage in the process, unless he went around collecting his passive.