Master Yi changes I'd like to see tested

Master Yi is in a weird balance state right now, quite bad except in low elo (unless you're doing some variation of the Taric mid strategy, in which case he's good in Challenger) so i'd like to propose some possible balance changes that mix buffs and nerfs. Meddler mentioned they're thinking of buffing him so I'd like to give my two cents.

• Change Highlander to additive movement speed. For those who don't know, Highlander is a unique movement speed buff that multiplies your total movement speed, unlike any other movespeed buff in the game. So it may be beneficial to remove this property and increase the numbers. That way his natural movement speed would less terrible at early levels, but he wouldn't go crazy with MS buffs from supports like Karma, Lulu, and Kayle.

• Change Double Strike so that it's a 3-hit effect (instead of 4-hit) but doesn't stack itself. This makes it better but it breaks the synergy it has with Phantom Hit from Rageblade.

• Remove the cast time on Alpha Strike, or just make it so Master Yi becomes untargetable as soon as the spell is cast. It's the only untargetability spell in the game with a cast time, and because of that it has a lot of weird interactions like being hit by spells while in Alpha Strike, or visibly being hit by CC only to disappear anyway.

• Narrow the variance in Alpha Strike's duration. For those who don't know, Alpha Strike makes Master Yi untargetable for between 0.25 and 0.8 seconds (roughly) depending on how many targets are struck by the animation. 0.25 is too short for dodging many spells (like skillshots with fat, slow hitboxes) and 0.8 is obnoxiously long when you're trying to gapclose, plus it's annoying for enemies when Yi spends so much time untargetable. My suggestion is to adjust his animations so that it gives something like between 0.4 and 0.6 seconds of untargetability.

• Give Highlander the Kai'Sa E treatment. Make it stronger (like more duration or movement speed, or lower the cooldown) but change the spell so that it takes a second to "charge" before activating, and during this time Master Yi can't attack. This makes Master Yi's initiation more telegraphed (counterplay!), makes timing Highlander more strategic, and in return he can have some more strength.