In regards to cast times, Electrical Surge I could definitely see getting a cast time reduction or even removal. However, the cast time on Thundering Shuriken needs to stay in some form, even if it gets reduced a bit, because his opponents needs his cast time in order to play against Kennen. If there are no minions in the way, W passive auto, Q, W is a guaranteed stun now, while on live, you can still dodge the Q because of the cast time. This is especially problematic against a lot of melee champions that Kennen used to be able to bully without much contest, as they have even less of a possibility to trade against Kennen.
Range indicator on Electrical Surge is a cool idea, and works as a nice QoL buff.
Slicing Maelstrom could use a target prioritization, but rather than prioritizing targets marked with his passive first, I think it should prioritize unmarked targets because it offers a lot of more interesting gameplay.
Your current teamfight rotation with Kennen is to Lightning Rush in, and then Slicing Maelstrom.
If it prioritized champions marked with his passive, it means that his ultimate would prioritize the front line tanks that he Lightning Rushed through, and ideally Kennen wants to be damaging the squishies that are dealing all of the enemy team's damage, although there is the exception of Kennen getting a good flank off.
However, if it prioritized unmarked champions, Kennen would be able to Lightning Rush through the front line, ult, and the prioritization would hit the unmarked back line of the enemy team, which is what Kennen wants to hit. His ability to flank also doesn't get changed too much because if Kennen plays it right, he would be out or range of the enemy front line, and Kennen would still be able to deal tons of damage to the enemy back line.
Making it prioritize unmarked champs also adds a lot more to Kennen, as Kennen would be able to reliably get a five man Electrical Surge on the enemy team, while if he wants to focus a target down in the way that prioritizing marked targets would, he could just Thundering Shuriken the target he wants to hit.
