Shyvana fan here, I agree that Shyvana needs buffs but giving her hard CC is not the answer. Instead of covering up Shyvana's weaknesses (which just homogenizes her), we should be making her do the things she already does well better.
Currently, Shyvana is a champion who can be viable without squeezing anyone else out, because she has the damage of a bruiser and the bulk of a tank without the CC brought by both of the other two examples. Giving her CC would confuse her niche with the bruisers, forcing her to compete with them. While this change would make her easier to balance against the other bruisers, it would also inevitably lead to Shyvana being marginalized; when both Shyvana and J4 bring strong hard initiation, but it takes 6 seconds of sticking to an enemy for Shyvana to outdamage J4 (which will never happen in today's meta), why pick Shyvana?
The correct route to making Shyvana viable-hell, to making most junglers viable in the current metagame, is niche-based balancing. By making Shyvana the best champion in the game at one specific thing, we ensure that she'll always be viable without pushing anyone else out. In Shyvana's case, her most notable attribute is her combination of bulk and damage in Dragon form. The best way to make her more powerful without making her encroach on any other junglers' space is to increase her bulk in Dragon form. It's not hidden power because the cause is incredibly obvious: you're fighting a motherfucking dragon.
Increasing Shyvana's bulk further while maintaining her current amounts of damage would carve her a niche as a different sort of tank. Sejuani, Nautilus, and Amumu are all meant to draw focus using their large amounts of sustained crowd control. Shyvana, on the other hand, should draw focus from the enemy using her extremely high damage potential and being a motherfucking dragon.