Not needed. That makes her entirely irrelevent in team fights.
Why do I say this? Let's compare to another hated champ: Zed.
Ahh, Zed; the classic pinnacle of complaints among Bronzies.
He ults in, effectively destroys a carry with zero effort, and safely gets out then is able to rejoin the team to poke and provide utility. Sure, he doesn't have all-in kill potential anymore, but he's still useful.
Kat on the other hand is already so easily shut down by ANY form of hard CC it isn't funny. So she fills the role of the most effective janitor we have.
Sure, she has amazing engage and a great way to mop up those fights with the resets resulting in free movement from shunpo.
HOWEVER, you take away her resets and push them down to only if you've damaged the enemy within 3 seconds (basically a reduced Darius ult) that means she needs to get hit by literally one form of hard CC (soraka E, Morg Q, etc) and she's entirely shut down and locked down and becomes 100% useless (provided you haven't blown her defenseless ass up). Now, God forbid you move a little too far apart for her in a team fight and you leave a member behind, she becomes again, useless for nearly 10 seconds during which you can engage freely. She has comparatively almost no poke, doesn't have the range to be poking, and certainly doesn't have any utility in doing so.
She's already feed or famine, why make it SO much worse she becomes nearly unplayable?