Some Potential Juggernauts
How about Renekton for a start? The whole point is that he can stomp mobile fighters like Riven, and that he can out-duel other juggernauts in the early game (i.e. Nasus)
Shyvana can also be a great juggernaut, and so would Olaf, but isn't Riot already working on them?
A few more champs that could be awesome juggernauts could be:
Aatrox- He has a lot of problems right now, even with the new items. Maybe do something to help him scale with HP so that he can be a better tank
Volibear- He's already kind of juggernauty (is that a new word?), but maybe some love to help him be more realistic as a pick in the top lane (where does he even go?)
Yorick (?)- Sounds like he could be a great juggernaut with a good rework. Slow movement, but a lot of slows to catch up, and a bit of a twist with his ult
Singed- He has needed a touch-up in a long while because he is frankly not used very often, and his kit is very awkward in the meta. Maybe give him a more Juggernaut-like rework and people would be encouraged to play him top :)
IDK, these are the few guys I can think of. If there's anyone else, mention it.
I feel like there are a lot of potential juggernauts (or guys who are already juggs) like Hecarim or Trundle, but feel free to help me out with the list :D