Just watching a stream of Jayce I don't even understand how you're supposed to gank him. Like at all. He is probably the fastest champion in the game with on demand speed boosts, leaps, and a knock back. Someone like Udyr can't even get close to him, and even if he does Udyr is just going to get knocked away.
How is this champion even real? He has both ranged and melee AOE. He has multiple forms of CC both soft and hard. He has poke. He has group utility with his speed boost. He has tons of built in stat boosts that give move speed, damage, and tankiness. Maybe he's not actually as good as I think he is but he seems pretty absurd.
What on earth are you talking about?
1. Udyr is a terrible ganker, one of the few junglers with absolutely no gap closer besides flash. Using him as an example is just laughable (plus if Udyr gets in range for the knockback then he has a chance of stunning before the knockback happens).
2. The jump is ONLY an offensive move, not to wards or minions or anything. It can slow, yes, but you have to jump into someone's face and then try to run away while they're slowed. Someone with a root or stun or nuke should be able to hit you after you close the distance unless you use jump + knockback to harass (I'm not sure if I tried this combo much). Compared to someone like Katarina, Ahri, Jax, Lee Sin, maybe Riven etc. those champions have even more escape besides speed boost. *edit* If someone ganks behind you you can jump to them, so I correct myself on this as it could be used as escape in this fashion.
3. The hard CC you mention is the short range knockback. It is not a stun like many top laners, nor long range like Ahri.
From my own playing, I imagine he will be nerfed because of everyone complaining (though I guess everyone almost always complains about new champions), but he seems relatively balanced because of two weaknesses -- no stun and no escape besides speed boost. If you stick to ranged form and play like an AD carry then it might work ok, but then you don't get the defensive boosts.
Don't forget that Graves was a ranged AD carry that got tanky stat boosts, had a slow, a gap closer that worked on offense or defense and could go through walls, and could completely prevent the enemy from seeing anything in the game.
Oh, and the other weakness, no ult/finisher. Compared to someone like Riven, Caitlyn, Graves, Miss Fortune, Darius, most AP carries, etc., he has to rely on pokes and sustained damage.
He does actually seem rather fun to play, which is rare for me, so I guess I should hope that he remains somewhat viable if he does get nerfed into the ground so he can still be fun without people hating you for choosing him.