So...good things first. This is a fantastic Visual Update concept: it is immediately obvious who the character is, and is incredibly well executed -- even down to nice little features like the lightning bolts on his ear stripes.
Now the bad: you've gotten the porporations VERY wrong for a Yordle.
Take a look at Tristana
The new Yordles have heads significantly wider than their shoulders, and shorter than they are wide -- you hit the first part (although it could stand to be bigger still), but the head height/width ratio you have is much more human.
The ears are positioned lower, starting JUST above the line of the jaw -- you can see this in Gnar as well. They tend to go out to the sides more than back as well.
The entire torso is only slightly taller than a Yordle's head, whereas your Kennen's torso looks to be about a head and a half. Yordle legs are likewise short -- slightly less than a head seems to be the case for Gnar and Tristana. Arms and hands are large for the frame -- falling below the knee in Gnar and Trist, with fairly long forearms for the total length of the limb -- you have the bulk in the upper arm instead, with the hands getting narrower.
I'd also personally cut the yellow highlights from the white sections of the outfit (it doesn't show up well in-game), and drop the pockets entirely -- they're not very Ionian.
All that said though? Fantastic job. With the anatomy edits and a bit of tweaking on the outfit specifics this would be absolutely incredible.