Next 3 Juggernaut Updates need to be Dr. Mundo, Volibear and Trundle
List of all current Juggernaut Characters according to Riot's definitions:

They all lack clear strengths or reasons to bring them to a team over other characters and all have the exact same playstyles that warranted Morde/Garen/Darius/Skarner to get updated
Mundo and Volibear need to be more than just walking health stackers. Getting % Total AD ratios would really help give them actual build paths beyond just stacking health. Neither character is really a "Tank" since they bring no utility, they are just bruisers with no real offensive scaling so they are forced to stack health and resists.
Trundle didn't see any rise in power or popularity during the entirety of the tank meta because he brings nothing to a team. Sure he can steal resists and health, which is great and all, but he was still useless against the majority of tanks.
Volibear is the AS version of Garen in a lot of ways and I see no reason why he needs to keep Mana. You should be constantly worried about having to duel him, because scary lightning bear.
Trundle should be even more about territory control and pushing. Give him actual reasons to be picked other than "yeah he can steal like 20 AD from characters he can never reach and Ult 1 out of 3 tanks on a team"
Mundo should be the epitome of meat shield and be an ever present threat to everyone. He gets stronger the more you try to kill him. He is like the beefier version of Olaf. Olaf wants to scrap, Mundo wants to Mundo.